Coupled Inductors Inverter Topology

ABSTRACT

A multi-level inverter topology is disclosed. A power converter circuit converts a DC source at its input to provide an alternating current (AC) at its output. The power converter circuit may have a controller operably attached to multiple series connections of switches. The controller may control one or more of the multiple series connections of switches to convert a DC input to provide multi-level AC voltages with DC offset across two terminals of the power converter circuit. The multi-level AC voltages with DC offset may then be converted by use of a plurality of series connections of switches to provide a single-phase AC voltage at a first output terminal with respect to at least one of a neutral potential, an earth potential, or a terminal of the power converter circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 17/148,322, filed Jan. 13, 2021, which is anon-provisional of and claims priority to U.S. Provisional PatentApplication No. 62/961,377, filed Jan. 15, 2020, each of which is herebyincorporated by reference in its entirety.

BACKGROUND

A multilevel inverter is a power electronic device that is capable ofproviding a desired alternating current (AC) voltage level at itsoutput. The desired AC voltage output is output by conversion of one ormore input direct current (DC) voltage levels at the multilevel inverterinput. A multilevel inverter with three or more output voltage levelsmay provide a combined voltage (Vout) at its output. Compared to aninverter with two levels of voltage combined together at its output, thecombined voltage (Vout) of the multilevel inverter may have a lowerdifferential change in voltage with respect to time. The lowerdifferential change in voltage may therefore provide a lower harmonicdistortion of the combined voltage (Vout). The lower harmonic distortionof the combined voltage (Vout) may therefore provide an increasedsmoothness of the combined voltage (Vout). Increased smoothness of thecombined voltage (Vout) may be proportional to the increase in thenumber of output voltage levels. However, the smoother combined voltage(Vout) of the multilevel inverter may demand a controller with increasedcomplexity. The increased number of output voltage levels may alsofurther demand an increased number of components for the realization ofthe multilevel inverter. The increased number of components may includemore switches when compared to the inverter with two levels of voltagecombined together at its output. The inverter with two levels of voltagecombined together at its output may require a controller with lesscomplexity.

SUMMARY

The following summary is a short summary of some of the inventiveconcepts for illustrative purposes only, and is not intended to limit orconstrain the inventions and examples in the detailed description.

Illustrative embodiments disclosed herein may be with respect to powersources in a power system, which may include the interconnection ofvarious groups of power sources. Each group of power sources may containdifferent types of power derived from renewable energy sources andnon-renewable energy sources. The renewable energy sources may beprovided from photovoltaic (PV) systems, wind or wave power. Examples ofnon-renewable energy sources may include fuel used to drive turbines orgenerators, for example.

Illustrative embodiments disclosed herein may include a power systemutilized to supply power to a load and/or a storage device. The powersystem may include various inter connections of groups of direct current(DC) power sources that also may be connected in various series,parallel, series parallel and parallel series combinations, for example.Some illustrative embodiments may involve the connection of DC sourcesto a power converter circuit to provide an alternating current (AC) onits output. The power converter circuit may be a multi-level invertertopology, which may include a pair of input terminals and a first seriesconnection of a first capacitor and a second capacitor. The first seriesconnection may be connected across the pair of input terminals. Aconnection of the first capacitor to the second capacitor may be at afirst terminal. A second series connection may include a first switch, asecond switch, a third switch and a fourth switch connected in series.The second series connection may be connected across the pair of inputterminals. A connection of the first switch to the second switch may beat a second terminal. And a connection of the second switch to the thirdswitch may be at a third terminal. A connection of the third switch tothe fourth switch may be at a fourth terminal. The first terminal mayconnect to the third terminal.

A plurality of other series connections of two or more switches may beconnected across the second terminal and the fourth terminal. Each ofthe plurality of other series connections of two or more switches maycomprise an intermediate (e.g., central) node. A respective inductor maybe coupled to each of the intermediate (e.g., central) nodes, connectedbetween the intermediate node and a (e.g., output) terminal, configuredto combine the voltages of the intermediate (e.g., central) node.

The (e.g., output) terminal configured to combine the voltages of theintermediate (e.g., central) nodes may be a single-phase output withrespect to at least one of a neutral potential, an earth potential, oranother terminal of the power converter circuit. The output terminal ofthe power converter circuit may be powered by converting a DC inputvoltage connected to the pair of input terminals to an AC outputvoltage.

Each of the respective inductors may have mutual inductance with atleast one of the other inductors. The power converter circuit mayfurther include a controller operably attached and configured tocontrol, by pulse width modulated (PWM) signals, each of the switches ofthe second series connection, and each of the plurality of other seriesconnections of two or more switches, which may be connected across thesecond terminal and the fourth terminal. The controller may be operableto convert, using the second series connection, a DC input voltageconnected to the pair of input terminals to provide multi-level ACvoltages with DC offset (with respect to at least one of the pair ofinput terminals) across the second terminal and the fourth terminal.

The controller may measure/sense the current flowing through the coupledinductors and may control, by changing the PWM signals, switches (e.g.,MOSFETs/IGBTs) to balance the currents flowing through theinductors/legs.

In some aspects, the coupled inductors may be coupled to the outputterminal through relays. The controller may use relays for connectingthe power converter circuit (e.g., an inverter) to a grid/load. Therelays may also function as a circuit breaker and/or a protectivemechanism to prevent high current/voltage or unintentional feeding ofthe electrical device into a sub grid or a stand-alone grid, oftenreferred to as an anti-islanding operation. Based on an interruption(e.g., the grid “going down”) or a fault detection, the controller mayoperate the relays to disconnect the output terminal from the grid/loadto ensure safety and to prevent damage to the electrical circuit or thegrid.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescription, claims, and drawings. The present disclosure is illustratedby way of example, and not limited by, the accompanying figures.

FIG. 1 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 2 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 3 illustrates a timing diagram of an electrical circuit accordingto aspects of the disclosure.

FIG. 4 illustrates a timing diagram of an electrical circuit accordingto aspects of the disclosure.

FIG. 5 illustrates a block diagram according to aspects of thedisclosure.

FIG. 6 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 7 illustrates a timing diagram of an electrical circuit accordingto aspects of the disclosure.

FIG. 8 illustrates waveforms associated with electrical circuitsaccording to aspects of the disclosure.

FIG. 9 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 10 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 11 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 12 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 13 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 14 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

FIG. 15 illustrates a diagram of an electrical circuit according toaspects of the disclosure.

DETAILED DESCRIPTION

In the following description of various aspects of the disclosure,reference is made to the accompanying drawings, which form a parthereof, and in which is shown, by way of illustration, variousembodiments in which aspects of the disclosure may be practiced. It isto be understood that other embodiments may be utilized and structuraland functional modifications may be made, without departing from thescope of the present disclosure.

Features of one or more aspects disclosed herein may relate to a powerconverter circuit (e.g., multilevel inverter). The power convertercircuit may be capable of providing a desired alternating current (AC)voltage level at its output from direct current (DC) voltage applied toits input. The power converter circuit may be realized by a multi-levelinverter circuit topology. The desired AC voltage output is output fromconversion of multiple DC voltage levels via an intermediate converterincluded in the multi-level inverter circuit topology.

The term “PWM” as used herein is with respect to the operation ofswitches described below. Unless otherwise stated, the term “PWM” refersto an active use of a switch for a period of time. The active use of theswitch during the period of time may include the switch being opened andclosed repeatedly during the time period. The term “ON” as used hereinwith respect to the operation of switches described below, refers to theactive use of a switch during a time period. When a switch is “ON”, theswitch remains substantially closed for an “ON” time period. The term“OFF” as used herein is with respect to the operation of switchesdescribed below and refers to active use of a switch during the timeperiod. When a switch is “OFF”, the switch remains substantially openfor an “OFF” time period.

The term “multiple” as used here in the detailed description indicatesthe property of having or involving several parts, elements, or members.The claim term “a plurality of” as used herein in the claims sectionfinds support in the description with use of the term “multiple” and/orother plural forms. Other plural forms may include for example regularnouns that form their plurals by adding either the letter ‘s’ or ‘es’ sothat the plural of converter is converters or the plural of switch isswitches, for example.

The claim terms “comprise”, “comprises” and/or “comprising” as usedherein in the claims section finds support in the description with useof the terms “may”, “include”, “includes” “including”, etc.

The terms, “substantially”, and, “about”, used herein include variationsthat are equivalent for an intended purpose or function (e.g., within apermissible variation range). Certain ranges are presented herein withnumerical values being preceded by the terms “substantially” and“about”. The terms “substantially” and “about” are used herein toprovide literal support for the exact number that it precedes, as wellas a number that is near to or approximately the number that the termprecedes. In determining whether a number is near to or approximately aspecifically recited number, the near or approximating unrequited numbermay be a number, which, in the context in which it is presented,provides the substantial equivalent of the specifically recited number.

All values are examples, and are not meant to be taken as limiting.Also, all given values include values that are substantially equal tothe given values. For example, a given value of 100 A can include anyvalue that would be operationally equivalent, e.g., about 99.5 A, 101 A,98.5 A, etc.

Reference is made to FIG. 1 , which illustrates a circuit diagram of apower converter circuit 10 according to illustrative aspects of thedisclosure. FIG. 1 provides an example of a multi-level inverter circuittopology. Thus, in the example embodiment of FIG. 1 , the powerconverter circuit 10 is an example of a multilevel inverter. A directcurrent (DC) input voltage Vin may be applied across input terminals Aand B. Input voltage Vin may be a DC voltage received from one or moreDC power sources, e.g. a battery, a photovoltaic panel, a rectifiedsource of alternating current (AC) from an AC generator, etc.

In some aspects, power converter circuit 10 may comprise a controller80, for example: a digital signal processing (DSP) circuit, a fieldprogrammable gate array (FPGA) device, etc. Controller 80 may controlpower converter circuit 10 and its components (for example, switches,voltages, etc.) based on a predetermined algorithm, a measured parameter(e.g., a measurement collected by one or more sensors), a calculatedparameter, determined or estimated (e.g., based on one or more measuredparameters) parameter, any other appropriate data, etc. As an example,the electrical parameter may be: current, voltage, power, frequency,etc. In some aspects, controller 80 may comprise sensors to measure orsense one or more electrical parameters.

A series connection of capacitors C1 and C2 may be connected acrossinput terminals A and B. In some aspects, capacitors C1 and C2 may bereplaced by a plurality of series and/or parallel connected capacitors.Node E may be the point of connection between capacitors C1 and C2(e.g., intermediate node). Node E may be coupled to neutral and/or earthpotential.

A series connection of switches Sa1, Sa2, Sa3 and Sa4 may also beconnected across input terminals A and B. A first terminal of switch Salmay be coupled to input terminal A and a second terminal of switch Sa1may be coupled to node C. A first terminal of switch Sa2 may be coupledto node C and a second terminal of switch Sa2 may be coupled to node F.Node F may be coupled to node E directly so that Nodes E and F have thesame electric potential. A first terminal of switch Sa3 may be coupledto node F and a second terminal of switch Sa3 may be coupled to node D.A first terminal of switch Sa4 may be coupled to node D and a secondterminal of switch Sa4 may be coupled to input terminal B.

A plurality of series connections of two or more switches may beconnected across nodes C and D. For example, circuit 10 of FIG. 1comprises N (e.g., N≥2) series connections of two switches, such thateach one the series connections are coupled in parallel with respect toeach other. A series connection of switches Sb1 and Sb2 may be connectedacross nodes C and D. A terminal of Sb1 and a terminal of Sb2 may becoupled to intermediate (e.g., central) node IN₁. As shown in FIG. 1 ,intermediate node IN₁ is a central node between two of the switches (Sb1and Sb2) belonging to one of the series connections. If the seriesconnection had three switches, intermediate node IN₁ could be the nodebetween the first and second switches or between second and thirdswitches. A series connection of switches Sb3 and Sb4 may also beconnected across nodes C and D. A terminal of Sb3 and a terminal of Sb4may be coupled to intermediate node IN₂. A series connection of switchesSb5 and Sb6 may also be connected across nodes C and D. A terminal ofSb5 and a terminal of Sb6 may be coupled to intermediate node IN₃. Aseries connection of switches Sb_((2N−1)) and Sb_(2N) may also beconnected across nodes C and D. A terminal of Sb_((2N−1)) and a terminalof Sb_(2N) may be coupled to intermediate node IN_(N).

A corresponding first terminal of inductors L1, L2, L3 . . . L_(N) maybe coupled to node J (e.g., an output terminal) and a correspondingsecond terminal of inductors L1, L2, L3 . . . L_(N) may be coupledrespectively to terminals IN₁, IN₂, IN₃ . . . IN_(N). Terminal J maycombine the voltages of the output legs. In some aspects, terminal J maybe an output terminal of power converter circuit 10 that may output anAC sine wave (e.g., with DC offset). For example, terminal J may be anoutput terminal of one phase in a single-phase/three-phase/multi-phaseconverter. Inductors L1, L2, L3 . . . L_(N) may be mutually coupledtogether. Inductors L1, L2, L3 . . . L_(N) may be utilized to smooth asine-wave of an AC output of power converter circuit 10.

Controller 80 may control switches Sa1, Sa2, Sa3 and Sa4. Switches Sa1,Sa2, Sa3 and Sa4 may be switched at a first frequency. The firstfrequency may be the output frequency (e.g., grid frequency, loadfrequency, utility frequency, (power) line frequency, 50 Hz-60 Hz,etc.). Switches Sa1 and Sa3 may be closed/turned ON/conductingsubstantially at the same time, and may be open/turnedOFF/non-conducting substantially at the same time (e.g., switches Sa1and Sa3 may be controlled in a corresponding manner, for example, basedon a common control signal). Switches Sa2 and Sa4 may be closed/turnedON/conducting substantially at the same time, and may be open/turnedOFF/non-conducting substantially at the same time (e.g., switches Sa2and Sa4 may be controlled in a corresponding manner, for example basedon a common signal) and in a complementary manner with regard toswitches Sa1 and Sa3 (e.g., when switches Sa1 and Sa3 are closed, Sa2and Sa4 may be open).

Controller 80 may control switches Sb1, Sb2, Sb3, Sb4, Sb5, Sb6 . . .Sb_((2N−1)), Sb_(2N). Switches Sb1, Sb2, Sb3, Sb4, Sb5, Sb6 . . .Sb_((2N−1)), Sb_(2N) may be switched at a second frequency. The secondfrequency may be higher than the first frequency. Switch Sb1 may beswitched in a complementary manner with regard to switch Sb2. Forexample, switch Sb1 may be closed/turned ON/conducting when switch Sb2is open/turned OFF/non-conducting, and switch Sb1 may be open/turnedOFF/non-conducting when switch Sb2 is closed/turned ON/conducting.Switch Sb3 may be switched in a complementary manner with regard toswitch Sb4. Switch Sb5 may be switched in a complementary manner withregard to switch Sb6. Switch Sb_((2N−1)) may be switched in acomplementary manner with regard to switch Sb_(2N). Also, in anembodiment with more than two switches in any one series connection, twoor more of the switches may be switched (like Sb_((2N−1))) in acomplementary manner with regard to the remaining switches of thatseries connection (like Sb_(2N)). In some aspects, switches Sb1, Sb3,Sb5 . . . Sb_(2N) may be switched in a phase-shifted manner. Forgeneralization, in a circuit comprising a plurality of N seriesconnections of two or more switches, each series connection may beswitched with phase-shift of 360°/N with respect to each other. Forexample, where N=3 the switches may be switched with phase-shift of120°.

For example, the switches of power converter circuit 10 of FIG. 1 (Sa1,Sa2, Sa3, Sa4, Sb1, Sb2, Sb3, Sb4, Sb5, Sb6 . . . Sb_((2N−1)), Sb_(2N))may be insulated gate bipolar transistors (IGBTs), metal oxidesemiconductor field effect transistors (MOSFETs), bipolar junctiontransistors (BJTs), field effect transistors (FETs), silicone-controlledrectifiers (SCRs) or any known solid-state switch, or any combination ofthese components.

In some aspects, switches Sb1, Sb2, Sb3, Sb4 Sb5, Sb6 . . . Sb_((2N−1)),Sb_(2N) may be switched according to the duty cycle ratio (which may bechanged according to a comparison between a reference voltage and theoutput voltage Vout), where each group (e.g., pair) of series-connectedswitches (e.g., where Sb1-Sb2 is the first pair, Sb3-Sb4 is the secondpair, Sb5-Sb6 is the third pair . . . and Sb_((2N−1))-Sb_(2N) is then^(th) pair) is shifted sequentially by 1/N (where N is the number ofseries connections) of the switching period with respect to the othergroups (e.g., pairs) of series-connected switches. The specific timingshown in FIGS. 3-4 may be an example of the desired duty cycles, but avariety of different timings may be used that may have similar ordifferent switching performance.

Reference is now made to FIG. 2 , which illustrates a diagram ofelectrical circuit 20 (e.g., multilevel inverter), an example of powerconverter circuit 10 of FIG. 1 , according to aspects of the disclosure.In FIG. 2 , inductors L1, L2, L3 of FIG. 1 may be replaced by mutuallycoupled inductors L4, L5, L6. Controller 80 of FIG. 1 may be replaced bycontroller 180.

As shown in FIG. 2 , in some aspects, switches Sa1, Sa2, Sa3 and Sa4 ofFIG. 1 are insulated gate bipolar transistors (IGBTs).

For example, electrical circuit 20 comprises IGBTs Sc1, Sc2, Sc3 andSc4. Controller 180 may control the gate (g) of IGBTs Sc1, Sc2, Sc3 andSc4. The collector (c) of IGBT Sc1 may be coupled to input terminal A.At node C, the emitter (e) of IGBT Sc1 may be coupled to the collector(c) of IGBT Sc2. At node F, the emitter (e) of IGBT Sc2 may be coupledto the collector (c) of IGBT Sc3. Node F may be coupled to node E. Atnode D, the emitter (e) of IGBT Sc3 may be coupled to the collector (c)of IGBT Sc4. The emitter of IGBT Sc4 may be coupled to input terminal B.

As shown in FIG. 2 , in some aspects, switches Sb1, Sb2, Sb3, Sb4, Sb5,Sb6 of FIG. 1 are metal oxide semiconductor field effect transistors(MOSFETs).

FIG. 2 also shows that the number N of series connections of two or moreswitches may be three (e.g., N=3). Accordingly, the three seriesconnections including switches Sb1, Sb2, Sb3, Sb4, Sb5, Sb6 in FIG. 1are replaced by six MOSFETs M1, M2, M3, M4, M5 and M6 in FIG. 2 .Controller 180 may control each one of MOSFETs M1, M2, M3, M4, M5 andM6. Each one of MOSFETs M1, M2, M3, M4, M5 and M6 may be an n-typeenhancement metal-oxide-semiconductor field-effect transistor comprisingdrain, source and gate terminals (denoted D, S and G respectively). Inthis example, controller 180 may control the voltage difference betweenthe source and gate terminals of MOSFETs M1, M2, M3, M4, M5 and M6.

The source terminals (S) of MOSFETs M1, M3 and M5 may be coupled to nodeC. At node IN₁ the drain terminal (D) of MOSFET M1 may be coupled to thesource terminal (S) of MOSFET M2. At node IN₂ the drain terminal (D) ofMOSFET M3 may be coupled to the source terminal (S) of MOSFET M4. Atnode IN₃ the drain terminal (D) of MOSFET M5 may be coupled to thesource terminal (S) of MOSFET M6. The drain terminals (D) of MOSFETs M2,M4 and M6 may be coupled to node D.

In some aspects of the disclosure herein, controller 180 may operateMOSFETs M1, M2, M3, M4, M5 and M6 at a first frequency (e.g. highfrequency), based on a modulation scheme that may include pulse widthmodulation (PWM), frequency modulation (FM), or a variable frequencyplus variable pulse width modulation, for example. The modulation schememay optimize spectrum and reduce ripple based on space vector (SV)modulation, types of phase disposition (PD) modulation, alternate phaseopposition disposition (APOD) modulation, various multicarrier PWMstrategies for multilevel inverters, etc. Controller 180 may operateIGBTs Sc1, Sc2, Sc3 and Sc4 at a second frequency (e.g. low frequency).The second frequency may be the load frequency, utility frequency,(power) line frequency, etc. In some aspects, the first frequency may behigher than the second frequency. For example, the first frequency maybe 500 Hz, 1 kHz, 5 kHz, 25 kHz, 100 kHz, 500 kHz, 1 MHz, etc. and thesecond frequency may be 50 Hz, 60 Hz, 500 Hz, etc.

In some aspects of the disclosure herein, mutually coupled inductors L4,L5, L6 may be coupled to terminal J optionally through additionalcircuit elements. Terminal J may combine the voltages at the output ofthe legs of (e.g., filter) inductors L4, L5, L6. For example, in FIG. 2, coupled inductors L4, L5, L6 may be coupled to terminal J throughrelays R1, R2 and R3, respectively. In some aspects, a (e.g., filter)capacitor may be coupled to one terminal of mutually coupled inductorsL4, L5, L6 (e.g., the terminal of the inductors L4, L5, and L6 that iscoupled with relays R1, R2 and R3, respectively). For example, in FIG. 2, capacitor C4 may be coupled between a terminal of inductor L4 and nodeK, capacitor C5 may be coupled between a terminal of inductor L5 andnode L, and capacitor C6 may be coupled between a terminal of inductorL6 and node M. Nodes K, L, M may be coupled to nodes having a differentvoltage levels or to one or more nodes having a same voltage level.Further, one or more of nodes K, L, M may be coupled to a node ofelectrical circuit 20 having a reference voltage (e.g., node E) oranother node having another voltage reference, such as neutral and/orearth potential. In FIG. 2 , inductor L7 (e.g., differential filter) maybe coupled/connected between terminal J and node N. A single-phase ACoutput/sine wave with DC offset of power converter circuit 10 may beprovided across capacitors C4, C5 and C6. An AC output voltage Vout maybe applied across capacitors C4, C5 and C6. AC output voltages Vout1,Vout2, and Vout3 may be applied across capacitors C4, C5, and C6,respectively. AC output voltages Vout1, Vout2, and Vout3 may be similarat the second frequency and phase shifted at the first frequency by120°.

In some aspects, capacitors C4, C5 and C6 may be replaced by a capacitor(or a plurality of capacitors) connected between terminal J and areference terminal (e.g., node E).

In aspects of the disclosure herein, one or more of relays R1, R2 and R3may comprise two or more relay contacts that may be provided using amulti-pole relay module. A multi-pole relay module incorporates aplurality of relays in a single package. A multi-pole relay module mayenable the use of a common control coil for more than one relay contact,thereby reducing the size and the costs of the system. For example, adual-pole relay module may have two contacts controlled by a singlecontrol coil so that a second control coil is not required, therebyreducing the relay array size, the dissipated energy during operation,the manufacturing costs, and/or the like.

In aspects of the disclosure herein, one or more of relays R1, R2 and R3may use a different electrical contact configuration (e.g., single-polesingle-throw (SPST), single-pole double-throw (SPDT), double-polesingle-throw (DPST)). For example, when the relay array comprises two ormore relays, using a DPST relay (e.g., a pair of switches or relaysactuated by a single coil) may reduce the consumed energy for drivingthe control coils of the relay.

In some aspects of the disclosure, controller 180 may measure/sense orreceive estimations and/or determinations (e.g., measurements collectedby sensors) and/or data, of one or more electrical parameters of circuit20. For example, controller 180 may measure/sense the current flowingthrough each one of inductors L4, L5, L6. The currentmeasurement/sensing of the current flowing through the coupled inductorsL4, L5, L6 may be used, by controller 180, to balance the leg (e.g.,inductors L4, L5, L6) currents. The current balance may be achieved bychanging the PWM signals that may control the switches/MOSFETs/IGBTs.Current balance between the legs (e.g., inductors L4, L5, L6) maydivide/split/control the output current of electrical circuit 20 in asubstantially equal way between each of the output legs/inductors L4,L5, L6. By virtue of the current balance between the legs, each ofrelays R1, R2 and R3 may be configured to conduct a lower peak currentthan if the leg currents were not balanced, thereby reducing the sizeand the costs of the system. For example, in a case where the outputcurrent of electrical circuit 20 is rated to a current at level of 30A,the current balance may ensure that a current of no more than 10A isflowing through each of the relays R1, R2 and R3. Thus, a configurationof the electrical circuit 20 using lower-rated relays may be enabled byvirtue of the current balance.

In some aspects of the disclosure, controller 180 may measure thecurrent flowing through coupled inductors L4, L5, L6 (e.g., differentialcurrent) and L7, voltage across capacitors C4, C5, C6, C1, and C2, etc.Based on detection of a differential current above a predeterminedlevel, controller 180 may vary its control to amend the differentialcurrent (e.g., by changing the PWM signals).

Controller 180 may use relays R1, R2 and R3 for connecting electricalcircuit 20 (e.g., an inverter, a power converter) to a grid/load. Therelays R1, R2 and R3 may also function as a circuit breaker and/or aprotective mechanism to prevent high current/voltage or unintentionalfeeding of the electrical device into a sub grid or a stand-alone grid,often referred to as an anti-islanding operation. Based on aninterruption (e.g., the grid “going down”) or a fault detection, relaysR1, R2 and R3 may disconnect electrical circuit 20 from the grid/load toensure safety and to prevent damage to electrical circuit 20 or thegrid. Relays R1, R2 and R3 may be coupled with the outputs of orincorporated into electrical circuit 20.

Reference is now made to FIG. 3 , which illustrates timelines 30 showingwaveforms that describe, according to some aspects of the disclosure, apossible control method of a power converter circuit (e.g., powerconverter circuit 10 and electrical circuit 20 of FIGS. 1 and 2respectively). The upper graph shows a waveform, in volts (V) versustime, for output voltage Vout. Output voltage Vout may be any one of ACoutput voltages Vout1, Vout2, and Vout3 of FIG. 2 , with respect to areference voltage (e.g., node E, neutral potential terminal, an earthpotential terminal). Output voltage Vout in FIG. 3 may be the outputpower of power converter circuit 10 and electrical circuit 20 of FIGS. 1and 2 , respectively. In some aspects, Vout may be filtered by a filtercircuit comprising a capacitor to generate a substantially AC sinusoidalvoltage waveform at the output of the filter circuit. In the exampleshown in FIG. 3 , output voltage Vout may be a 50 Hz sine-waveform of230V_(RMS). Graphs PWM1, PWM2, PWM3, PWM4 and PWM5 may represent PWMcontrol signals used to control switches of the power converter circuit.The PWM1, PWM2, PWM3, PWM4 and PWM5 signals may be generated by digitalencoding component(s) (e.g., a microprocessor) and/or analog circuit(s)(e.g., using a comparator, oscillator, etc.). For example, PWM1, PWM2,PWM3, PWM4 and PWM5 signals may be generated by controller 80 of FIG. 1or controller 180 of FIG. 2 .

In the example shown in FIG. 3 , signals PWM1 and PWM2 may be relativeto the frequency of output voltage Vout, e.g., 50 Hz. Signals PWM1 andPWM2 may be complementary with respect to each other. For example,signal PWM1 may be applied to control switches Sa1/Sa3 of FIG. 1 and/orthe gate terminals (g) of IGBTs Sc1/Sc3 of FIG. 2 . Signal PWM2 may beapplied to control switches Sa2/Sa4 of FIG. 1 and/or the gate terminals(g) of IGBTs Sc1/Sc3 of FIG. 2 .

In the example shown in FIG. 3 , signals PWM3, PWM4 and PWM5 may beconfigured to control switches to be switched all during the same cycle.For example, signal PWM3 may control the gate terminal (G) of MOSFET M1of FIG. 2 , signal PWM4 may control the gate terminal (G) of MOSFET M3of FIG. 2 , and signal PWM5 may control the gate terminal (G) of MOSFETM5 of FIG. 2 . A complementary PWM signal with respect to signal PWM3may control the gate terminal (G) of MOSFET M2 of FIG. 2 , acomplementary PWM signal with respect to signal PWM4 may control thegate terminal (G) of MOSFET M4 of FIG. 2 , and a complementary PWMsignal of signal PWM5 may control the gate terminal (G) of MOSFET M6 ofFIG. 2 .

In the example, signals PWM3, PWM4 and PWM5 may control each of theswitches/MOSFETs to be switched at 3 kHz. This allows each switch/MOSFETto turn ON for a period, according to the duty cycle ratio (which may bechanged according to a comparison between a reference voltage and theoutput voltage Vout), where each of the signals PWM3, PWM4 and PWM5 maybe shifted sequentially by 1/N (where N is the number of seriesconnections of switches/MOSFETs (for example, MOSFETs M1-M2, MOSFETsM3-M4, MOSFETs M5-M6), which in the example shown in FIG. 3 is three(N=3)) of the switching period, such as ⅓ kHz or around 333.33microseconds. During this time each switch turns ON and OFF. This mayeffectively increase the effective frequency to 3 times the switchingperiod at the output terminal (e.g., terminal J of FIG. 2 ) of the powerconverter circuit 10 or electrical circuit 20 of FIGS. 1 and 2 ,respectively, without actually increasing the switching frequency.However, in embodiments described herein, the MOSFETs may be switched ata much higher rate (e.g., 200 kHz).

Further, the design may be scalable in that the effective frequency canbe increased more and more by increasing the number of seriesconnections of switches; the multi-level switching in each seriesconnections of switches allows the switching to increase an effectivefrequency (e.g., relative to the switching frequency) of the currentflowing through the differential filter (e.g., inductor L7 of FIG. 2 )without driving a single MOSFET faster. Signals PWM1 and PWM2 may becomplementary with respect to each other. For example, signal PWM1 maybe applied to control switches Sa1/Sa3 of FIG. 1 and/or the gateterminals (g) of IGBTs Sc1/Sc3 of FIG. 2 . Signal PWM2 may be applied tocontrol switches Sa2/Sa4 of FIG. 1 and/or the gate terminals (g) ofIGBTs Sc2/Sc4 of FIG. 2 .

Reference is now made to FIG. 4 , which illustrates timelines showingwaveforms that describe, according to some aspects of the disclosure, apossible method of generating a pulse width modulation (PWM).

The example shown in FIG. 4 , illustrates timelines 40 describing apossible method of generating a pulse width modulation (PWM) signal PWM3of FIG. 3 .

The upper graph shows a waveform, in volts (V) versus time, for outputvoltage Vout. Output voltage Vout may be any one of AC output voltagesVout1, Vout2, and Vout3 of FIG. 2 , with respect to a reference voltage(e.g., node E, neutral potential terminal, an earth potential terminal)and equivalent with Vout shown in FIG. 3 . Output voltage Vout may bethe output power of power converter circuit 10 and electrical circuit 20of FIGS. 1 and 2 , respectively. In some aspects, Vout may be filteredby a filter circuit comprising a capacitor to generate a substantiallyAC sinusoidal voltage waveform at the output of the filter circuit. Inthe example shown in FIG. 4 , output voltage Vout may be a 50 Hzsine-waveform of 230V_(RMS).

The second graph from the top of FIG. 4 may represent a reference signalCOM corresponding to (e.g., related to) output voltage Vout. During thepositive half of the sine-wave Vout, reference signal COM may be similarto output voltage Vout (e.g., a sine wave with substantially the samefrequency but with a different amplitude). During the negative half ofthe sine-wave Vout, reference signal COM may be complementary to outputvoltage Vout. For example, reference signal COM may be equivalent with1−(Vout/Vamp), where Vamp is the peak amplitude of sine-wave Vout.

The third graph from the top of FIG. 4 may represent another referencesignal REF3 used to compare with the reference signal COM. In someaspects, REF3 may be a saw tooth wave (or saw wave). In the example, thesaw tooth wave REF3 may have a frequency of 3 kHz.

The lower graph shows PWM control signal PWM3 used to control aswitch(s) of the power converter circuit. For example, signal PWM3 maycontrol switch Sb1 of FIG. 1 and/or the gate terminal (G) of MOSFET M1of FIG. 2 and may be equivalent with control signal PWM3 of FIG. 3 .Control signal PWM3 may be generated by digital encoding component(s)(e.g., a microprocessor) and/or analog circuit(s) (e.g., using acomparator, oscillator, etc.). In this example control signal PWM3 maybe generated by a comparator receiving reference signals COM and REF3 asinputs. Where reference signal COM is larger than reference signal REF3,control signal PWM3 may be ‘1’ indicating an ‘ON’ state. Where referencesignal COM is smaller than reference signal REF3, control signal PWM3may be ‘0’ indicating an ‘OFF’ state.

The PWM control signal PWM3 may be generated by digital encodingcomponent(s) (e.g., a microprocessor) and/or analog circuit(s) (e.g.,using a comparator, oscillator, etc.). For example, PWM control signalPWM3 signals may be generated by controller 80 of FIG. 1 or a similarone.

Reference is now made to FIG. 5 , which illustrates a block diagram of acontroller according to aspects of the disclosure herein. Controller 80of FIG. 1 and/or controller 180 of FIG. 2 may be implemented withcontroller 280. A controller 280 may include at least one of amicroprocessor, microcontroller, digital signal processor (DSP), or thelike. Controller 280 may be connected to a memory 289. Controller 280may serve as a central controller to other similar controllers ascontroller 280 which may be included to control multiple interconnectedpower converter circuits (e.g., a plurality of power converter circuits10 for example). Communications interface 282 connected to controller280 may provide communications between controller 280 and othercontrollers (and other communication interfaces) included generally in apower system, which includes power converter circuit 10. Thecommunications to and from communications interface 282 may be based ona control algorithm running on controller 280. The communications mayinclude control signals provided on control lines which operably connectto and control power converter circuit 10. For example, controller 280may generate control signals to control the switches of power convertercircuit 10 of FIG. 1 (Sa1, Sa2, Sa3, Sa4, Sb1, Sb2, Sb3, Sb4, Sb5, Sb6 .. . Sb_((2N−1)), Sb_(2N)) and/or the IGBTs and MOSFETs of powerconverter circuit 10 of FIG. 1 (IGBTs Sc1, Sc2, Sc3 and Sc4 and MOSFETsM1, M2, M3, M4, M5 and M6).

Communications through communications interface 282 may also includemeasured and/or sensed parameters via sensors/sensor interface 284 that,for example, may be included in power converter circuit 10 of FIG. 1 .The communications by communications interface 282 may be conveyed usingWiFi, power line communications (PLC), near field communications or aRS232/485 communication bus, for example. Communications interface 282may communicate with a local area network or cellular network in orderto establish an internet connection. For example, the internetconnection may provide a feature of remote monitoring or reconfigurationof power converter circuit 10.

A display 288 connected to central controller 280 may be mounted on thesurface of the housing used to house power converter circuit 10 forexample. Display 288 may display for example the power produced frompower converter circuit 10. Controller 280 may be connected to ashutdown device 286 (e.g., a safety and remote shutdown device). Sensingby sensor(s)/sensor interface 284 as well as sensed parameterscommunicated between controller 280 and sensor(s)/sensor interfaces ofpower converter circuit 10 may be indicative of a fault condition (e.g.,overvoltage, overcurrent, ground fault, failure of components, inputpower or load disconnection). Upon detection of the fault condition,shutdown device 286 may be activated in order to isolate the faultcondition and/or shutdown power converter circuit 10. For example, insuch a case, controller 180 of FIG. 2 may turn OFF relays R1, R2 and R3.

Control signals from controller 280 applied to the switches of powerconverter circuit 10 of FIG. 1 (Sa1, Sa2, Sa3, Sa4, Sb1, Sb2, Sb3, Sb4,Sb5, Sb6 . . . Sb_((2N−1)), Sb_(2N)) and/or the IGBTs and MOSFETs ofelectrical circuit 20 of FIG. 2 (IGBTs Sc1, Sc2, Sc3 and Sc4 and MOSFETsM1, M2, M3, M4, M5 and M6) are generated using a modulation scheme. Themodulation scheme may be responsive to the electrical parameters sensedin power converter circuit 10 when power converter circuit 10 may ormight not be connected to a load. The load may be an AC motor or autility grid supply for example. The modulation scheme may include pulsewidth modulation (PWM), frequency modulation (FM), or a variablefrequency plus variable pulse width modulation, for example. Analgorithm of controller 280 may allow application of control signals.The control signals may be applied responsive to a sensing step of analgorithm to sense the electrical parameters in power converter circuit10 connected to a load and/or when power converter circuit 10 is notconnected to a load. For example, sensor(s)/sensor interface 284 maysense/measure the current flowing through the output legs/mutuallycoupled inductors L4, L5, L6. The load may be a utility grid, forexample.

In some aspects of the disclosure herein, controller 280 of FIG. 5 maybe implemented as an independent circuit or component. Theimplementation may be digital (e.g. using a microprocessor), analog(e.g. using an integrator), or both (e.g., using a digital-analogconverter).

Reference is made to FIG. 6 , which illustrates a circuit diagram of apower converter circuit 30 according to illustrative aspects of thedisclosure. FIG. 6 provides an example of a multi-level inverter circuittopology. Thus, in the example embodiment of FIG. 6 , the powerconverter circuit 30 is an example of a three-phase multilevel inverter.A direct current (DC) input voltage Vin may be applied across inputterminals A and B. Input voltage Vin may be a DC voltage received from aDC power source, e.g. a battery, a photovoltaic panel, a rectifiedsource of alternating current (AC) from an AC generator, etc.

A series connection of capacitors C1 and C2 may be connected acrossinput terminals

A and B. In some aspects, capacitors C1 and C2 may be replaced by aplurality of series and/or parallel connected capacitors. Node E may bethe point of connection between capacitors C1 and C2 (e.g., intermediatenode). Node E may be coupled to neutral and/or earth potential.

In some aspects, power converter circuit 30 may comprise a plurality ofsingle-phase power converter circuits. Thus, in the example embodimentof FIG. 6 , the power converter circuit 30 comprises three single-phaseconverter circuits 11, 21 and 31. In the example embodiment of FIG. 6 ,each of single-phase converter circuits 11, 21 and 31 are similar topower converter circuit 10 of FIG. 1 . Each of the single-phaseconverter circuits 11, 21 and 31 may be connected across input terminalsA and B and configured to receive direct current input voltage V_(in).Each of the single-phase converter circuits 11, 21 and 31 may beconnected to node E. Each of the single-phase converter circuits 11, 21and 31 may be configured to convert direct current input voltage V_(in)to an alternating current.

Power converter circuit 11 may comprise: a series connection of switchesSd1, Sd2, Sd3 and Sd4 (e.g., similar to switches Sa1, Sa2, Sa3 and Sa4of FIG. 1 ) that may also be connected across input terminals A and B,and a plurality of series connections of switches M1, M2, M3, M4, M5 andM6 (e.g., similar to switches Sb1, Sb2, Sb3, Sb4, Sb5 and Sb6 of FIG. 1) that may be connected across nodes C and D. In the example embodimentof FIG. 6 , switches Sd1, Sd2, Sd3 and Sd4 may be insulated gate bipolartransistors (IGBTs) and switches M1, M2, M3, M4, M5 and M6 may beMOSFETs (e.g., similar to FIG. 2 ). Each series connection of switchesM1, M2, M3, M4, M5 and M6 may comprise an intermediate node; the seriesconnection of switches M1-M2 may comprise intermediate node IN₁₁, theseries connection of switches M3-M4 may comprise intermediate node IN₁₂,and the series connection of switches M5-M6 may comprise intermediatenode IN₁₃. Within power converter circuit 11, a corresponding firstterminal of inductors L11, L12, and L13 may be coupled to node J1 (e.g.,an output terminal) and a corresponding second terminal of inductorsL11, L12, and L13 may be coupled respectively to terminals IN₁₁, IN₁₂,and IN₁₃. Terminal J1 may combine the voltages of the output legs. Insome aspects, terminal J1 may be an output terminal of power convertercircuit 11 that may output an AC sine wave (e.g., with DC offset). Forexample, terminal J1 may be an output terminal of one phase in asingle-phase/three-phase/multi-phase converter. Inductors L11, L12, andL13 may be mutually coupled together. Inductors L11, L12, and L13 may beutilized to smooth a sine-wave of an AC output of power convertercircuit 11. In some embodiments, inductor L111 (e.g., differentialfilter) may be coupled/connected between terminal J1 and terminal P1. Insuch embodiment, terminal P1 may be an output terminal of one phase in asingle-phase/three-phase/multi-phase converter. In some aspects, acapacitor may be coupled between terminal J1 and a reference terminal(e.g., node E).

Power converter circuit 21 may comprise: a series connection of switchesSd5, Sd6, Sd7 and Sd8 (e.g., similar to switches Sa1, Sa2, Sa3 and Sa4of FIG. 1 ) that may also be connected across input terminals A and B,and a plurality of series connections of switches M11, M12, M13, M14,M15 and M16 (e.g., similar to switches Sb1, Sb2, Sb3, Sb4, Sb5 and Sb6of FIG. 1 ) that may be connected across nodes C and D. In the exampleembodiment of FIG. 6 , switches Sd5, Sd6, Sd7 and Sd8 may be insulatedgate bipolar transistors (IGBTs) and switches M11, M12, M13, M14, M15and M16 may be MOSFETs (e.g., similar to FIG. 2 ). Each seriesconnection of switches M11, M12, M13, M14, M15 and M16 may comprise anintermediate node; the series connection of switches M11-M12 maycomprise intermediate node IN₂₁, the series connection of switchesM13-M14 may comprise intermediate node IN₂₂, and the series connectionof switches M15-M16 may comprise intermediate node IN₂₃. Within powerconverter circuit 21, a corresponding first terminal of inductors L21,L22, and L23 may be coupled to node J2 (e.g., an output terminal) and acorresponding second terminal of inductors L21, L22, and L23 may becoupled respectively to terminals IN₂₁, IN₂₂, and IN₂₃. Terminal J2 maycombine the voltages of the output legs. In some aspects, terminal J2may be an output terminal of power converter circuit 21 that may outputan AC sine wave (e.g., with DC offset). For example, terminal J2 may bean output terminal of one phase in asingle-phase/three-phase/multi-phase converter. Inductors L21, L22, andL23 may be mutually coupled together. Inductors L21, L22, and L23 may beutilized to smooth a sine-wave of an AC output of power convertercircuit 21. In some embodiments, inductor L121 (e.g., differentialfilter) may be coupled/connected between terminal J2 and terminal P2. Insuch embodiment, terminal P2 may be an output terminal of one phase in asingle-phase/three-phase/multi-phase converter. In some aspects, acapacitor may be coupled between terminal J2 and a reference terminal(e.g., node E).

Power converter circuit 31 may comprise: a series connection of switchesSd9, Sd10, Sd11 and Sd12 (e.g., similar to switches Sa1, Sa2, Sa3 andSa4 of FIG. 1 ) that may also be connected across input terminals A andB, and a plurality of series connections of switches M21, M22, M23, M24,M25 and M26 (e.g., similar to switches Sb1, Sb2, Sb3, Sb4, Sb5 and Sb6of FIG. 1 ) that may be connected across nodes C and D. In the exampleembodiment of FIG. 6 , switches Sd9, Sd10, Sd11 and Sd12 may beinsulated gate bipolar transistors (IGBTs) and switches M21, M22, M23,M24, M25 and M26 may be MOSFETs (e.g., similar to FIG. 2 ). Each seriesconnection of switches M21, M22, M23, M24, M25 and M26 may comprise anintermediate node; the series connection of switches M21-M22 maycomprise intermediate node IN₃₁, the series connection of switchesM23-M24 may comprise intermediate node IN₃₂, and the series connectionof switches M25-M26 may comprise intermediate node IN₃₃. Within powerconverter circuit 31, a corresponding first terminal of inductors L31,L32, and L33 may be coupled to node J3 (e.g., an output terminal) and acorresponding second terminal of inductors L31, L32, and L33 may becoupled respectively to terminals IN₃₁, IN₃₂, and IN₃₃. Terminal J3 maycombine the voltages of the output legs. In some aspects, terminal J3may be an output terminal of power converter circuit 31 that may outputan AC sine wave (e.g., with DC offset). For example, terminal J3 may bean output terminal of one phase in asingle-phase/three-phase/multi-phase converter. Inductors L31, L32, andL33 may be mutually coupled together. Inductors L31, L32, and L33 may beutilized to smooth a sine-wave of an AC output of power convertercircuit 31. In some embodiments, inductor L131 (e.g., differentialfilter) may be coupled/connected between terminal J3 and terminal P3. Insuch embodiment, terminal P3 may be an output terminal of one phase in asingle-phase/three-phase/multi-phase converter. In some aspects, acapacitor may be coupled between terminal J3 and a reference terminal(e.g., node E).

Controller 380 may be: a digital signal processing (DSP) circuit, afield programmable gate array (FPGA) device, etc. Controller 380 maycontrol power converter circuit 30 and its components (for example,switches, voltages, etc.) based on a predetermined algorithm, a measuredparameter (e.g., a measurement collected by one or more sensors), acalculated parameter, determined or estimated (e.g., based on one ormore measured parameters) parameter, any other appropriate data, etc. Asan example, the electrical parameter may be: current, voltage, power,frequency, etc. In some aspects, controller 380 may comprise sensors tomeasure or sense one or more electrical parameters.

Controller 380 may control switches Sd1, Sd2, Sd3, Sd4, Sd5, Sd6, Sd7,Sd8, Sd9, Sd10, Sd11, Sd12, M1, M2, M3, M4, M5, M6, M11, M12, M13, M14,M15, M16, M21, M22, M23, M24, M25 and M26. The switches M1, M2, M3, M4,M5, M6, M11, M12, M13, M14, M15, M16, M21, M22, M23, M24, M25 and M26may be insulated gate bipolar transistors (IGBTs), metal oxidesemiconductor field effect transistors (MOSFETs), bipolar junctiontransistors (BJTs), filed effect transistors (FETs), assilicone-controlled rectifiers (SCRs) or any known solid-state switch,or any combination of these components.

Switches Sd1, Sd2, Sd3, Sd4, Sd5, Sd6, Sd7, Sd8, Sd9, Sd10, Sd11, andSd12 may be switched at a first frequency. The first frequency may bethe output frequency (e.g., grid frequency, load frequency, utilityfrequency, (power) line frequency, 50 Hz-60 Hz, etc.). Each switch ineach pair of switches Sd1+Sd3, Sd2+Sd4, Sd5+Sd7, Sd6+Sd8, Sd9+Sd11,Sd10+Sd12, may be closed/turned ON/conducting substantially at the sametime, and may be open/turned OFF/non-conducting substantially at thesame time. Each pair of the pairs of switches Sd1+Sd3, Sd5+Sd7, andSd9+Sd11 may be switched at the same time and in a complementary mannerwith regard to the pairs of switches Sd2+Sd4, Sd6+Sd8, and Sd10+Sd12respectively (e.g., when pair of switches Sd1+Sd3 are closed, the pairof switches Sd2+Sd4 may be open).

The pairs of switches Sd1+Sd3 and Sd2+Sd4 may be switched in a 120°phase (of the first frequency) with respect to pairs of switches Sd5+Sd7and Sd6+Sd8, and may be switched in a 240° phase (of the firstfrequency) with respect to pairs of switches Sd9+Sd11 and Sd10+Sd12.

Switches M1, M2, M3, M4, M5, M6, M11, M12, M13, M14, M15, M16, M21, M22,M23, M24, M25 and M26 may be switched at a second frequency. The secondfrequency may be higher than the first frequency. Each switch ofswitches M1, M3, M5, M11, M13, M15, M21, M23, and M25 may be switched ina complementary manner with regard to switch M2, M4, M6, M12, M14, M16,M22, M24, and M26 respectively. For example, switch M1 may beclosed/turned ON/conducting when switch M2 is open/turnedOFF/non-conducting, and switch M1 may be open/turned OFF/non-conductingwhen switch M2 is closed/turned ON/conducting.

For generalization, in a power converter circuit comprising a pluralityof N series connections of two or more switches, each group (e.g., pair)of series-connected switches (e.g., where M1-M2 is the first pair, M3-M4is the second pair, M5-M6 is the third pair . . . and M_((2N−1))-M_(2N)is the n^(th) pair) is shifted sequentially by 1/N (where N is thenumber of series connections) of the switching period of the secondfrequency with respect to the other groups (e.g., pairs) ofseries-connected switches. For example, power converter circuits 11, 21and 31 comprise three (N=3) series connections of switches, thus eachseries connection of switches may be switched with phase-shift of 120°.

In some aspects, each group (e.g., pair) of the groups (e.g., pairs) ofseries-connected switches of all power converter circuits may be shiftedsequentially by 1/(P*N) (where P is the number of parallel connectedpower converters) of the switching period of the second frequency withrespect to the other groups (e.g., pairs) of series-connected switches.

For example, in FIG. 6 where P=N=3, the switches M1, M2, M3, M4, M5, M6,M11, M12, M13, M14, M15, M16, M21, M22, M23, M24, M25 and M26 may beswitched according to following sequential phase-shifting of the secondfrequency (e.g., higher-frequency):

Pair of switches M1- M3- M5- M11- M13- M15- M21- M23- M25- M2 M4 M6 M12M14 M16 M22 M24 M26 Phase- 0° 120° 240° 40° 160° 280° 80° 200° 320°shift

The phase shifting between each pair of the pairs of series-connectedswitches of all single-phase power converter circuits (e.g.,single-phase converter circuits 11, 21, and 31) may enable a powerconverter (e.g., power converter circuit 30) to achieve lower rippleinput current and lower voltage fluctuations over the input capacitance(e.g., capacitors C1 and C2 of FIGS. 1, 2 and 6 ).

In some aspects, the sequential phase shifting at the second frequencyof the switches may reduce the temporary and mean (e.g., average) inputcurrent drawn by the power converter circuit (for example, powerconverter circuit 30) according to illustrative aspects of thedisclosure. Thus, the ripple voltage across the bulk/input capacitors(e.g., capacitors C1 and C2) may be reduced. The reduction of ripplevoltage and/or current flowing through the bulk/input capacitors mayreduce the cost and size of a power converter circuit.

Switches M1, M2, M3, M4, M5, M6, M11, M12, M13, M14, M15, M16, M21, M22,M23, M24, M25 and M26 may be switched according to the duty cycle ratio,which may be changed according to a comparison between a referencevoltage and the output voltage at output terminals P1, P2 and P3. Insome aspects, the reference voltage of the switches of series connectionof switches (e.g., Sd1, Sd2, Sd3, and Sd4) may be similar to thereference voltage of the switches of the same power converter circuit(e.g., switches M1, M2, M3, M4, M5, and M6). An example for the timingshown in FIGS. 3-4 may be an example of the desired duty cycles, but avariety of different timings may be used that may have similar ordifferent switching performance.

Reference is made to FIG. 7 , which illustrates timelines 70 showingwaveforms that describe, according to some aspects of the disclosure, apossible control method of a power converter circuit (e.g., powerconverter circuit 30 comprising three single-phase converter circuits11, 21 and 31). The timelines show waveforms, in volts (V) versus time,and illustrate an example for possible control signals. A differentgraph is provided for each of the control signals PWM11, PWM12, PWM13,PWM14 and PWM15 used to control switches of the power converter circuit.The PWM11, PWM12, PWM13, PWM14 and PWM15 control signals may begenerated by digital encoding component(s) (e.g., a microprocessor,general processor, etc.) and/or analog circuit(s) (e.g., using acomparator, oscillator, etc.). For example, PWM11, PWM12, PWM13, PWM14and PWM15 control signals may be generated by controller 380 of FIG. 6 .

In the example shown in FIG. 7 , control signals PWM11, PWM12, PWM13,PWM14 and PWM15 may be generated at the second frequency of FIG. 6 ,which is relatively higher than the first frequency, the switchingfrequency of the switches of the series connection of switches (e.g.,switches Sd1, Sd2, Sd3 and Sd4 of FIG. 6 ), and the frequency of theoutput voltage at output terminals P1, P2 and P3, e.g., 50 Hz. Controlsignals PWM11, PWM12, PWM13, PWM14 and PWM15 may be varied according tothe duty cycle ratio, which may be changed according to a comparisonbetween a reference voltage and the output voltage at output terminalsP1, P2 and P3.

Control signals PWM11, PWM14 and PWM15 may control switches of differentseries connections in a power converter, where all series connectionsmay be connected in parallel with respect to each other. For example,control signals PWM11, PWM14 and PWM15 may control the gate terminal (G)of MOSFETs M1, M3 and M5 of power converter circuit 11 in FIG. 6 ,respectively (or M11, M13 and M15 of power converter circuit 21 in FIG.6 , respectively, or M21, M23 and M25 of power converter circuit 31 inFIG. 6 , respectively). For instance, control signals PWM11, PWM14 andPWM15 may be similar to control signals PWM3, PWM4 and PWM5 of FIG. 3 .

Control signals PWM11, PWM14 and PWM15 may be shifted sequentially by1/(P) (where P is the number of parallel connected single-phase powerconverters) of the switching period of the second frequency with respectto each other. For example, in FIG. 6 , where P=3, control signalsPWM11, PWM14 and PWM15 may be shifted sequentially by 120°.

Control signals PWM11, PWM14 and PWM15 may be varied according to acommon duty cycle ratio, which may be changed according to a comparisonbetween a common reference voltage and the output voltage at the outputterminal of the single-phase power converter (e.g., terminal P1 ofsingle-phase power converter 11).

In some aspects, controller 380 of FIG. 6 may generate complementary PWMcontrol signals with respect to PWM control signals PWM11, PWM14 andPWM15. The complementary PWM control signals may control thecorresponding and complementary switch(es) to the series connection. Forexample, complementary PWM control signals with respect to PWM controlsignals PWM11, PWM14 and PWM15 may control the gate terminal (G) ofMOSFETs M2, M4 and M6 of FIG. 6 , respectively.

Control signals PWM11, PWM12 and PWM13 may control each of the switchesof different parallel-connected power converters. Following the aboveexample, where control signal PWM11 controls the gate terminal (G) ofMOSFET M1 of power converter circuit 11 in FIG. 6 , control signalsPWM12 and PWM13 may control the gate terminal (G) of MOSFETs M1l and M21of power converters 21 and 31 in FIG. 6 , respectively.

Control signals PWM11, PWM12 and PWM13 may be shifted sequentially by1/(P*N) (where P is the number of parallel connected power converters,and N is the number of parallel series connections in each powerconverter) of the switching period of the second frequency with respectto each other. For example, in FIG. 6 , where P=N=3, control signalsPWM11, PWM12 and PWM13 may be shifted sequentially by 40°.

Control signals PWM11, PWM12 and PWM13 may be varied according to adifferent duty cycle ratio, which may be changed according to acomparison between a common reference voltage and the output voltage atthe output terminal of the corresponding single-phase power converter.For example, the duty cycle ratio of control signal PWM11 may be changedaccording to a comparison between a common reference voltage and theoutput voltage at terminal P1 of single-phase power converter 11. Theduty cycle ratio of control signal PWM12 and PWM13 may be changedaccording to a comparison between a common reference voltage and theoutput voltage at terminal P2 of single-phase power converter 21 and P3of single-phase power converter 31, respectively. The output voltages ateach of terminals P1, P2 and P3 may be phase shifted by 120°, thus, theduty-cycle of each of control signals PWM11, PWM12 and PWM13 may vary.

Reference is made to FIG. 8 , which illustrates timelines 80 and 81showing waveforms that describe, according to some aspects of thedisclosure, a current flowing through the bulk/input capacitors of apower converter circuit (e.g., capacitors C1 and C2 of FIGS. 1, 2 and 6). The timelines show waveforms, in current (A) versus time.

Timeline 80 illustrates a current flowing through the bulk/inputcapacitors of a 3-phase power converter circuit using sequential phaseshifting (for example, as depicted referring to FIGS. 6 and 7 ) withrespect to each of the switches (within each phase and between eachphase).

Timeline 81 illustrates a current flowing through the bulk/inputcapacitors of a 3-phase power converter circuit with the sameconfiguration of elements as the power converter circuit of timeline 80.However, the current shown in timeline 81 illustrates an operationwithout the sequential phase-shifting at the high-frequency (e.g.,second frequency of FIGS. 1, 2, 3, 4 and 6 ) between differentsingle-phase power converters; although a high-frequency phase-shiftbetween different series connections within a single-phase powerconverter may exist, for example, as shown in FIG. 3 .

It can be noted, based on the comparison between the currentsillustrated in timelines 80 and 81, that the sequential phase shiftingmay achieve lower ripple input current, and, thus, lower voltagefluctuations over the input capacitance (e.g., capacitors C1 and C2 ofFIGS. 1, 2 and 6 ).

In some aspects, the sequential phase shifting of the switches mayreduce the temporary and mean (e.g., average) input current drawn by thepower converter circuit (for example, power converter circuit 30)according to illustrative aspects of the disclosure. The reduction ofripple voltage and/or current flowing through the bulk/input capacitorsmay reduce cost and size.

Reference is made to FIG. 9 , which illustrates a circuit diagram of apower converter circuit 95 according to illustrative aspects of thedisclosure. FIG. 9 provides a generalization of an (e.g., multi-level)inverter circuit topology according to illustrative aspects of thedisclosure. In the example embodiment of FIG. 9 , the power convertercircuit 95 is an example of a three-phase multilevel inverter. A directcurrent (DC) input voltage Vin may be applied across input terminals Aand B. Input voltage Vin may be a DC voltage received from a DC powersource, e.g. a battery, a photovoltaic panel, a rectified source ofalternating current (AC) from an AC generator, etc.

A series connection of capacitors C1 and C2 may be connected acrossinput terminals A and B. In some aspects, capacitors C1 and C2 may bereplaced by a plurality of series and/or parallel connected capacitors.Node E may be the point of connection between capacitors C1 and C2(e.g., intermediate node). Node E may be coupled to neutral and/or earthpotential.

In some aspects, power converter circuit 95 may comprise a plurality ofsingle-phase power converter circuits. In the example embodiment of FIG.9 , the power converter circuit 95 comprises three single-phaseconverter circuits 96, 97 and 98. Each of the single-phase convertercircuits 96, 97 and 98 may be connected across input terminals A and Band configured to receive direct current input voltage V_(in). Each ofthe single-phase converter circuits 96, 97 and 98 may be connected tonode E. Each of the single-phase converter circuits 96, 97 and 98 may beconfigured to convert direct current input voltage V_(in) to analternating current at a first frequency.

In the example embodiment of FIG. 9 , each of single-phase convertercircuits 96, 97 and 98 may comprise a plurality of switches (e.g.,switches Sa1-Sa4 and Sb1-Sb_(2N) of power converter circuit 10 of FIG. 1). The plurality of switches may be coupled in different configurations,for example according to the following topologies: neutral-point clamped(NPC), T-type neutral-point clamped (TNPC), active neutral-point clamped(ANPC), half-bridge (HB), flying-capacitor (FC), etc. The switches maybe insulated gate bipolar transistors (IGBTs), metal oxide semiconductorfield effect transistors (MOSFETs), bipolar junction transistors (BJTs),field effect transistors (FETs), silicone-controlled rectifiers (SCRs)or any known solid-state switch, or any combination of these components.

Controller 990 may be: a digital signal processing (DSP) circuit, afield programmable gate array (FPGA) device, etc. Controller 990 maycontrol power converter circuits 96, 97 and 98 and their components (forexample, switches, voltages, etc.) based on a predetermined algorithm, ameasured parameter (e.g., a measurement collected by one or moresensors), a calculated parameter, a determined or estimated (e.g., basedon one or more measured parameters) parameter, any other appropriatedata, etc. As an example, the electrical parameter may be: current,voltage, power, frequency, etc. In some aspects, controller 990 maycomprise sensors to measure or sense one or more electrical parameters.

Power converter circuits 96, 97 and 98 may comprise an inductor or aplurality of inductors coupled to an output terminal. In some aspects,power converter circuits 96, 97 and 98 may output at a correspondingoutput terminal an AC sine wave (e.g., with DC offset). The inductor maybe utilized to smooth a sine-wave of an AC output of a correspondingpower converter circuit. In case of a plurality of inductors, theinductors may be mutually coupled together.

Power converter circuit 96 may comprise a plurality of circuitscomprising N circuits: F1, F2, F3 . . . and FN. The plurality ofcircuits F1, F2, F3 . . . and FN may be connected across input terminalsA and B and configured to receive direct current input voltage V_(in).Each of the plurality of circuits F1, F2, F3 . . . and FN may beconnected to node E.

Power converter circuit 97 may comprise a plurality of circuitscomprising N circuits: G1, G2, G3 . . . and GN. The plurality ofcircuits G1, G2, G3 . . . and GN may be connected across input terminalsA and B and configured to receive direct current input voltage V_(in).Each of the plurality of circuits G1, G2, G3 . . . and GN may beconnected to node E.

Power converter circuit 98 may comprise a plurality of circuitscomprising N circuits: H1, H2, H3 . . . and HN. The plurality ofcircuits H1, H2, H3 . . . and HN may be connected across input terminalsA and B and configured to receive direct current input voltage V_(in).Each of the plurality of circuits H1, H2, H3 . . . and HN may beconnected to node E.

Each circuit of the plurality of circuits F1, F2, F3 . . . and FN,circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN may comprise asimilar configuration of elements (e.g., switches, capacitors,inductors, etc.). The configuration of elements may be according to oneor more of the following topologies: neutral-point clamped (NPC), T-typeneutral-point clamped (TNPC), active neutral-point clamped (ANPC),half-bridge (HB), flying-capacitor (FC), etc. Controller 990 may controlthe plurality of circuits F1, F2, F3 . . . and FN, circuits G1, G2, G3 .. . and GN, H1, H2, H3 . . . and HN at a second frequency correspondingto the selected configuration. In some aspects, the second frequency maybe similar to the first frequency.

Each circuit of the plurality of circuits of each power convertercircuit (for example each circuit of the plurality of circuits F1, F2,F3 . . . and FN) may be shifted sequentially by 1/N (where N is thenumber parallel-connected circuit) of the switching period (of thesecond frequency) with respect to the other circuits of the plurality ofcircuits.

The output voltage of power converter circuit 96 may be in a 120° phasewith respect to the output voltage of power converter circuit 97, and ina 240° phase (of the first frequency) with respect to output voltage ofpower converter circuit 98.

For generalization, in an inverter circuit comprising P parallelconnected power converters (e.g., power converters 96, 97 and 98)generating a sine-wave at a first frequency, where each power converterof the power converters comprises N circuits (e.g. F1, F2, F3 . . . andFN) controlled at a second frequency, each circuit (e.g. F1, F2, F3 . .. and FN) may be shifted sequentially by 1/(P*N) of the switching periodof the second frequency with respect to the other circuits of powerconverters (e.g. circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . andHN).

For example, power converter circuit (e.g., inverter) 95 comprises threepower converter circuits 96, 97 and 98, and thus P=3. Each of the threepower converter circuits 96, 97 and 98 comprises four (N=4) seriesconnections of switches, thus controller 990 may control each circuitwith phase-shift of 30°, according to following control scheme using asequential phase-shifting (of the second frequency):

Circuits F1 F2 F3 F4 G1 G2 G3 G4 H1 H2 H3 H4 Phase-shift 0° 90° 180°270° 30° 120° 210° 300° 60° 150° 240° 330°

The phase shifting between each circuit of all power converter circuitsmay enable the power converter circuit 95 to achieve lower ripple inputcurrent and lower voltage fluctuations over the input capacitance (e.g.,capacitors C1 and C2 of FIGS. 1, 2, 6 and 9 ).

In some aspects, the sequential phase shifting of the switches mayreduce the temporary and mean (e.g., average) input current drawn by thepower converter circuit (for example, power converter circuit 95)according to illustrative aspects of the disclosure. Thus, the ripplevoltage across the bulk/input capacitors (e.g., capacitors C1 and C2)may be reduced. The reduction of ripple voltage and/or current flowingthrough the bulk/input capacitors may reduce cost and size.

Reference is made to FIG. 10 , which illustrates a circuit diagram of apower converter circuit 90 according to illustrative aspects of thedisclosure. FIG. 10 provides a generalization of an (e.g., multi-level)inverter circuit topology according to illustrative aspects of thedisclosure. FIG. 10 may be an example of circuit 95 of FIG. 9 ,according to aspects of the disclosure. As shown in FIG. 10 , in someaspects of the disclosure, the circuits of each power converter circuitmight not be coupled to the middle point of connection betweencapacitors C1 and C2 (e.g., intermediate node). Thus, in FIG. 10 , theinput capacitance is shown by a single capacitor Cin, which may comprisea capacitor or a plurality of capacitors.

In some aspects, power converter circuit 90 may comprise a plurality ofsingle-phase power converter circuits. In the example embodiment of FIG.9 , the power converter circuit 90 comprises three single-phaseconverter circuits 96, 97 and 98. Each of the single-phase convertercircuits 91, 92 and 93 may be connected across input terminals A and Band configured to receive direct current input voltage V_(in). Each ofthe single-phase converter circuits 91, 92 and 93 may be configured toconvert direct current input voltage V_(in) to an alternating current ata first frequency.

In the example embodiment of FIG. 10 , each of single-phase convertercircuits 91, 92 and 93 may comprise a plurality of switches (e.g.,switches Sa1-Sa4 and Sb1-Sb_(2N) of power converter circuit 10 of FIG. 1). The plurality of switches may be coupled in different configurations,for example according to the following topologies: neutral-point clamped(NPC), T-type neutral-point clamped (TNPC), active neutral-point clamped(ANPC), half-bridge (HB), flying-capacitor (FC), etc. The switches maybe insulated gate bipolar transistors (IGBTs), metal oxide semiconductorfield effect transistors (MOSFETs), bipolar junction transistors (BJTs),field effect transistors (FETs), silicone-controlled rectifiers (SCRs)or any known solid-state switch, or any combination of these components.

Power converter circuit 91 may comprise a plurality of circuitscomprising N circuits: A1, A2, A3 . . . and AN. The plurality ofcircuits A1, A2, A3 . . . and AN may be connected across input terminalsA and B and configured to receive direct current input voltage V_(in).

Power converter circuit 92 may comprise a plurality of circuitscomprising N circuits: B1, B2, B3 . . . and BN. The plurality ofcircuits B1, B2, B3 . . . and BN may be connected across input terminalsA and B and configured to receive direct current input voltage V_(in).

Power converter circuit 93 may comprise a plurality of circuitscomprising N circuits: C1, C2, C3 . . . and CN. The plurality ofcircuits C1, C2, C3 . . . and CN may be connected across input terminalsA and B and configured to receive direct current input voltage V_(in).

Controller 980 may be: a digital signal processing (DSP) circuit, afield programmable gate array (FPGA) device, etc. Controller 980 maycontrol power converter circuits 91, 92 and 93 and their components (forexample, switches, voltages, etc.) based on a predetermined algorithm, ameasured parameter (e.g., a measurement collected by one or moresensors), a calculated parameter, a determined or estimated (e.g., basedon one or more measured parameters) parameter, any other appropriatedata, etc. As an example, the electrical parameter may be: current,voltage, power, frequency, etc. In some aspects, controller 980 maycomprise sensors to measure or sense one or more electrical parameters(e.g., current, voltage, resistance).

Controller 980 may control each circuit of the power converters (e.g.circuits A1, A2, A3 . . . and AN, B1, B2, B3 . . . and BN, B1, B2, B3 .. . and BN) according the control scheme depicted in reference to FIG. 9and controller 990.

For generalization, in an inverter circuit comprising P parallelconnected power converters (e.g., power converters 91, 92 and 93)generating a sine-wave at a first frequency, where each power converterof the power converters comprises N circuits (e.g. A1, A2, A3 . . . andAN) controlled at a second frequency, each circuit (e.g. A1, A2, A3 . .. and AN) may be shifted sequentially by 1/(P*N) of the switching periodof the second frequency with respect to the other circuits of powerconverters (e.g. circuits B1, B2, B3 . . . and BN, C1, C2, C3 . . . andCN).

For example, inverter 90 comprises three power converter circuits 91, 92and 93, thus P=3. Each of the three power converter circuits 91, 92 and93 comprises four (N=4) series connections of switches, thus controller980 may control each circuit with phase-shift of 30°, according tofollowing control scheme using a sequential phase-shifting (of thesecond frequency):

Circuits A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4 Phase-shift 0° 90° 180°270° 30° 120° 210° 300° 60° 150° 240° 330°

Reference is made to FIG. 11 , which illustrates a circuit diagram of anelectrical circuit (e.g., power converter) 110. Electrical circuit 110comprises circuit 111, which may be an example of each of circuits A1,A2, A3 . . . and AN, B1, B2, B3 . . . and BN, and C1, C2, C3 . . . andCN of FIG. 10 , according to aspects of the disclosure. In some aspects,circuit 111 may be a flying-capacitor converter or ANPC withflying-capacitors.

Circuit 110 includes electrical circuit (e.g., power converter) 111 andoutput inductor L1. Circuit 111 includes: a first plurality of switchesSw1, Sw2, Sw3 and Sw4, a second plurality of switches S1, S2, S3, S4 . .. S_(2N−1), S_(2N), S_(2N+1) and S_(2N+2), and a plurality of capacitorsC100, C101, C102 . . . and C10N.

Electrical circuit 111 may be connected across input terminals A and B.(e.g., similar to input terminals A and B of FIG. 10 ). Electricalcircuit 111 may convert the input direct-current (e.g., DC) voltageacross input terminals A and B to an output alternating-current (e.g.,AC) voltage at terminal OUT. Output inductor L110 may be connected toterminal OUT.

The first plurality of switches may be connected across input terminalsA and B. A first terminal of switch Sw1 may be coupled to input terminalA and a second terminal of switch Sw1 may be coupled to node C. A firstterminal of switch Sw2 may be coupled to node C and a second terminal ofswitch Sw2 may be coupled to node F. A first terminal of switch Sw3 maybe coupled to node F and a second terminal of switch Sw3 may be coupledto node D. A first terminal of switch Sw4 may be coupled to node D and asecond terminal of switch Sw4 may be coupled to input terminal B.

The second plurality of switches S1, S2, S3, S4 . . . S_(2N−1), S_(2N),S_(2N+1) and S_(2N+2) may comprise pairs of switches S1-S2, S3-S4 . . .S_(2N−1)-S_(2N), and S_(2N+1)-S_(2N+2). Capacitor C100 (or a pluralityof capacitors) may be coupled to node C and node D, and between pairs ofswitches S1-S2. Another capacitor (or a plurality of capacitors) may beconnected between two pairs of switches. For example, capacitor C101 maybe connected between pairs of switches S1-S2 and S3-S4, capacitor C102may be connected between pairs of switches S5-S6 (not shown), andcapacitor C10N may be connected between pairs of switchesS_(2N−1)-S_(2N), and S_(2N+1)-S_(2N+2). Terminal OUT may be connectedbetween pair of switches S_(2N+1)-S_(2N+2).

The first plurality of switches may be switched by a controller (e.g.,controller 980 of FIG. 10 ) at a first frequency. The first frequencymay be the output frequency of the voltage at terminal OUT. Switch Sw1may be switched and conduct simultaneously (e.g., at the same time) withswitch Sw3 during the positive half-cycle of the output voltage atterminal OUT. Switch Sw2 may be switched and conduct simultaneously(e.g., at the same time) with switch Sw4 during the negative half-cycleof the output voltage at terminal OUT.

The second plurality of switches may be switched by a controller (e.g.,controller 980 of FIG. 10 ) at a second frequency and according to aduty-cycle ratio of the output voltage at terminal OUT. The secondfrequency may be higher than the first frequency. Each two switches ofthe same pair of switches, may be switched (e.g., turned ON/conduct) ina complementary manner. For example, during the positive half-cycle ofthe output voltage at terminal OUT, switch S1 may be switched at aduty-cycle ratio D of the output voltage at terminal OUT, while switchS3 may be switched at 1-D. When switch S1 is OFF, switch S3 may be ON,and vice versa. During the negative half-cycle of the output voltage atterminal OUT, switch S3 may be switched at the duty-cycle ratio D of theoutput voltage at terminal OUT, while switch S1 may be switched at 1-D.

In some aspects of the disclosure, each pair of switches of the secondplurality of switches may be shifted sequentially by 1/N (where N is thenumber of pair of switches of the second plurality) of the switchingperiod of the second frequency.

In a case where circuit 111 is used for each of circuits A1, A2, A3 . .. and AN, B1, B2, B3 . . . and BN, and C1, C2, C3 . . . and CN of FIG.10 , all output terminals OUT of each circuit of the same powerconverter (e.g., A1, A2, A3 . . . and AN) may be coupled together, tothe same node of the output inductor of the corresponding powerconverter (for example, output inductor L110). In some aspects of thedisclosure herein, all output terminals OUT of each circuit of the samepower converter (e.g., A1, A2, A3 . . . and AN) may be coupled tomutually coupled inductors (e.g., coupled inductors L4, L5, L6 of FIG. 2), each of which is connected to an output inductor (e.g., differentialfilter), similar to output inductor L7 of FIG. 2 .

In some aspects, circuit 111 may function as a single-phase powerconverter. For example, circuit 111 may replace each of the single-phaseconverter circuits 91, 92 and 93.

Reference is made to FIG. 12 , which illustrates a circuit diagram of anelectrical circuit (e.g., power converter) 120. Electrical circuit 120comprises circuit 121, which may be an example of circuits F1, F2, F3 .. . and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , according to aspects of the disclosure. In some aspects,circuit 121 may be a neutral-point-clamped (e.g. NPC) converter.

Circuit 120 includes electrical circuit (e.g., power converter) 121 andoutput inductor L120. Circuit 121 includes: a plurality of S11, S12,S13, and S14, and diodes D1, and D2.

Electrical circuit 121 may be connected across input terminals A and B.(e.g., similar to input terminals A and B of FIG. 10 ). Electricalcircuit 121 may be configured to connect to node E, which may be anintermediate node (e.g., the point of connection) between capacitors C1and C2 of FIG. 9 . In some embodiments, node E may be coupled to neutraland/or earth potential.

Electrical circuit 121 may convert the input direct-current (e.g., DC)voltage across input terminals A and B to an output alternating-current(e.g., AC) voltage at a first frequency (e.g., 50/60 Hz) at terminalOUT. Output inductor L120 may be connected to terminal OUT.

The plurality of switches may be connected across input terminals A andB. A first terminal of switch S11 may be coupled to input terminal A anda second terminal of switch S11 may be coupled to node C. A firstterminal of switch S12 may be coupled to node C and a second terminal ofswitch S12 may be coupled to node F. A first terminal of switch S13 maybe coupled to node F and a second terminal of switch S13 may be coupledto node D. A first terminal of switch S14 may be coupled to node D and asecond terminal of switch S14 may be coupled to input terminal B.

The anode of the first diode D1 may be coupled to node E and the cathodeof the first diode D1 may be coupled to node C. The anode of the seconddiode D2 may be coupled to node D, and the cathode of the second diodeD2 may be coupled to node E.

Switches S12 and S13 of the plurality of switches may be switched by acontroller (e.g., controller 990 of FIG. 9 ) at a first frequency. Thefirst frequency may be the output frequency of the voltage at terminalOUT of electrical circuit 121 in FIG. 12 . Switches S12 and S13 may beswitched in a complementary manner. For example, during the positivehalf-cycle of the output voltage at terminal OUT, switch S12 may be ONand switch S13 may be OFF. During the negative half-cycle of the outputvoltage at terminal OUT, switch S13 may be ON and switch S12 may be OFF.

Switches S11 and S14 of the plurality of switches may be switched by acontroller (e.g., controller 990 of FIG. 9 ) at a second frequency. Thesecond frequency may be higher than the output frequency of the voltageat terminal OUT of electrical circuit 121 in FIG. 12 .

During the positive half-cycle of the output voltage at terminal OUT,switch S11 may be switched according to the duty-cycle ratio D of theoutput voltage. During the positive half-cycle of the output voltage atterminal OUT, switch S14 may be turned OFF. Thus, during the positivehalf-cycle, the first diode D1 may conduct in a complementary mannerwith respect to switch S11, e.g., at 1-D.

During the negative half-cycle of the output voltage at terminal OUT,switch S14 may be switched according to the duty-cycle ratio D of theoutput voltage. During the negative half-cycle of the output voltage atterminal OUT, switch S11 may be turned OFF. Thus, during the negativehalf-cycle, the second diode D2 may conduct in a complementary mannerwith respect to switch S14, e.g., at 1-D.

In a case where circuit 121 is used for each of circuits F1, F2, F3 . .. and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , all output terminals OUT of each circuit of the same powerconverter (e.g., F1, F2, F3 . . . and FN of power converter 96) may becoupled together, to the same node of the output inductor of thecorresponding power converter (for example, output inductor L120).

In a case where circuit 121 is used for each of circuits F1, F2, F3 . .. and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , each circuit of the same power converter (e.g., F1, F2, F3 . .. and FN of power converter 96) may be shifted sequentially by 1/N(where N is the number of circuits in the power converter) of theswitching period of the second frequency. In addition, each circuit ofeach power converter may be shifted sequentially by 1/N*P (where P isthe number of single-phase power converters, and N is the number ofcircuits in the power converter) of the switching period of the secondfrequency.

In some aspects of the disclosure herein, all output terminals OUT ofeach circuit of the same power converter (e.g., F1, F2, F3 . . . and FNof power converter 96) may be coupled to mutually coupled inductors(e.g., coupled inductors L4, L5, L6 of FIG. 2 ), each of which isconnected to an output inductor (e.g., differential filter), similar tooutput inductor L7 of FIG. 2 .

Reference is made to FIG. 13 , which illustrates a circuit diagram of anelectrical circuit (e.g., power converter) 130. Electrical circuit 130comprises circuit 131, which may be an example of circuits F1, F2, F3 .. . and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , according to aspects of the disclosure. In some aspects,circuit 131 may be a T-type neutral-point-clamped (e.g. TNPC) converter.

Circuit 130 includes electrical circuit (e.g., power converter) 131 andoutput inductor L130. Circuit 131 includes: a plurality of switches S21,S22, S23, and S24, and two diodes D11 and D12.

Electrical circuit 131 may be connected across input terminals A and B.(e.g., similar to input terminals A and B of FIG. 10 ). Electricalcircuit 131 may be configured to connect to node E, which may be anintermediate node (e.g., the point of connection) between capacitors C1and C2 of FIG. 9 . In some embodiments, node E may be coupled to neutraland/or earth potential.

Electrical circuit 131 may convert the input direct-current (e.g., DC)voltage across input terminals A and B to an output alternating-current(e.g., AC) voltage at a first frequency (e.g., 50/60 Hz) at terminalOUT. Output inductor L130 may be connected to terminal OUT.

A first terminal of switch S21 may be coupled to input terminal A and asecond terminal of switch S21 may be coupled to terminal OUT. A firstterminal of switch S22 may be coupled to node E and a second terminal ofswitch S22 may be coupled to node F. A first terminal of switch S23 maybe coupled to node F and a second terminal of switch S23 may be coupledto terminal OUT. A first terminal of switch S24 may be coupled toterminal OUT and a second terminal of switch S24 may be coupled to inputterminal B. Diode D11 may be coupled in parallel with switch S22, wherethe anode of D11 may be coupled to node E, and the cathode of D11 may becoupled to node F. Diode D12 may be coupled in parallel with switch S23,where the anode of D12 may be coupled to terminal OUT, and the cathodeof D12 may be coupled to node F.

Switches S22 and S23 of the plurality of switches may be switched by acontroller (e.g., controller 990 of FIG. 9 ) at a first frequency. Thefirst frequency may be the output frequency of the voltage at terminalOUT. Switches S22 and S23 may be switched in a complementary manner. Forexample, during the positive half-cycle of the output voltage atterminal OUT, switch S23 may be ON and switch S22 may be OFF. During thenegative half-cycle of the output voltage at terminal OUT, switch S22may be ON and switch S23 may be OFF.

Switches S21 and S24 may be switched by a controller (e.g., controller990 of FIG. 9 ) at a second frequency. The second frequency may behigher than the output frequency of the voltage at terminal OUT.

During the positive half-cycle of the output voltage at terminal OUT,switch S21 may be switched according to the duty-cycle ratio D of theoutput voltage. During the positive half-cycle of the output voltage atterminal OUT, switch S24 may be turned OFF. Thus, during the positivehalf-cycle, diode D11 may conduct in a complementary manner with respectto switch S21, e.g., at 1-D.

During the negative half-cycle of the output voltage at terminal OUT,switch S24 may be switched according to the duty-cycle ratio D of theoutput voltage. During the negative half-cycle of the output voltage atterminal OUT, switch S21 may be turned OFF. Thus, during the negativehalf-cycle, diode D12 may conduct in a complementary manner with respectto switch S24, e.g., at 1-D.

In a case where circuit 131 is used for each of circuits F1, F2, F3 . .. and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , all output terminals OUT of each circuit of the same powerconverter (e.g., F1, F2, F3 . . . and FN of power converter 96) may becoupled together, to the same node of the output inductor of thecorresponding power converter (for example, output inductor L130).

In a case where circuit 131 is used for each of circuits F1, F2, F3 . .. and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , each circuit of the same power converter (e.g., F1, F2, F3 . .. and FN of power converter 96) may be shifted sequentially by 1/N(where N is the number of circuits in the power converter) of theswitching period of the second frequency. In addition, each circuit ofeach power converter may be shifted sequentially by 1/N*P (where P isthe number of single-phase power converters, and N is the number ofcircuits in the power converter) of the switching period of the secondfrequency.

In some aspects of the disclosure herein, all output terminals OUT ofeach circuit of the same power converter (e.g., F1, F2, F3 . . . and FNof power converter 96) may be coupled to mutually coupled inductors(e.g., coupled inductors L4, L5, L6 of FIG. 2 ), each of which isconnected to an output inductor (e.g., differential filter), similar tooutput inductor L7 of FIG. 2 .

Reference is made to FIG. 14 , which illustrates a circuit diagram of anelectrical circuit (e.g., power converter) 140. Electrical circuit 140comprises circuit 141, which may be an example of circuits F1, F2, F3 .. . and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , according to aspects of the disclosure. In some aspects,circuit 141 may be an active neutral—point clamped (e.g., ANPC)converter.

Circuit 140 includes electrical circuit (e.g., power converter) 141 andoutput inductor L140. Circuit 141 includes: a first plurality ofswitches S31, S32, S33, and S34, and a second plurality of switches Ss1and Ss2.

Electrical circuit 141 may be connected across input terminals A and B.(e.g., similar to input terminals A and B of FIG. 10 ). Electricalcircuit 141 may be configured to connect to node E, which may be anintermediate node (e.g., the point of connection) between capacitors C1and C2 of FIG. 9 . In some embodiments, node E may be coupled to neutraland/or earth potential.

Electrical circuit 141 may convert the input direct-current (e.g., DC)voltage across input terminals A and B to an output alternating-current(e.g., AC) voltage at a first frequency (e.g., 50/60 Hz) at terminalOUT. Output inductor L140 may be connected to terminal OUT.

A first terminal of switch S31 may be coupled to input terminal A and asecond terminal of switch S31 may be coupled to node C. A first terminalof switch S32 may be coupled to node E and a second terminal of switchS32 may be coupled to node C. A first terminal of switch S33 may becoupled to node E and a second terminal of switch S33 may be coupled tonode D. A first terminal of switch S34 may be coupled to node D and asecond terminal of switch S34 may be coupled to input terminal B.

The first plurality of switches S31, S32, S33, and S34 may be switchedby a controller (e.g., controller 990 of FIG. 9 ) at a first frequency.The first frequency may be the output frequency of the voltage atterminal OUT. Switches S31 and S33 may be switched at the same time(e.g. simultaneously). Switches S32 and S34 may be switched in acomplementary manner with respect to switches S31 and S33. For example,during the positive half-cycle of the output voltage at terminal OUT,switches S31 and S33 may be ON and switches S32 and S34 may be OFF.During the negative half-cycle of the output voltage at terminal OUT,switches S32 and S34 may be ON and S31 and S33 may be OFF.

Switches Ss1 and Ss2 may be switched by a controller (e.g., controller990 of FIG. 9 ) at a second frequency. The second frequency may behigher than the output frequency of the voltage at terminal OUT.

During the positive half-cycle of the output voltage at terminal OUT,switch Ss1 may be switched according to the duty-cycle ratio D of theoutput voltage. During the positive half-cycle of the output voltage atterminal OUT, switch Ss2 may be switched in a complementary manner withrespect to switch Ss1, e.g., at 1-D.

During the negative half-cycle of the output voltage at terminal OUT,switch Ss2 may be switched according to the duty-cycle ratio D of theoutput voltage. During the negative half-cycle of the output voltage atterminal OUT, switch Ss1 may be switched in a complementary manner withrespect to switch Ss2, e.g., at 1-D.

In a case where circuit 141 is used for each of circuits F1, F2, F3 . .. and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , all output terminals OUT of each circuit of the same powerconverter (e.g., F1, F2, F3 . . . and FN of power converter 96) may becoupled together, to the same node of the output inductor of thecorresponding power converter (for example, output inductor L140).

In a case where circuit 141 is used for each of circuits F1, F2, F3 . .. and FN, circuits G1, G2, G3 . . . and GN, H1, H2, H3 . . . and HN ofFIG. 9 , each circuit of the same power converter (e.g., F1, F2, F3 . .. and FN of power converter 96) may be shifted sequentially by 1/N(where N is the number of circuits in the power converter) of theswitching period of the second frequency. In addition, each circuit ofeach power converter may be shifted sequentially by 1/N*P (where P isthe number of single-phase power converters, and N is the number ofcircuits in the power converter) of the switching period of the secondfrequency.

In some aspects of the disclosure herein, all output terminals OUT ofeach circuit of the same power converter (e.g., F1, F2, F3 . . . and FNof power converter 96) may be coupled to mutually coupled inductors(e.g., coupled inductors L4, L5, L6 of FIG. 2 ), each of which isconnected to an output inductor (e.g., differential filter), similar tooutput inductor L7 of FIG. 2 .

In some aspects of the disclosure herein, in case where a powerconverter (e.g., power converter 96 comprising F1, F2, F3 . . . and FN)comprises a plurality of parallel-connected circuits of circuit 141, thefirst plurality of switches S31, S32, S33, and S34 may be used for eachof the parallel-connected circuits. For example, circuit 10 of FIG. 1 isan example for a power converter comprising N parallel-connectedcircuits, similar to circuit 141. The series connection of switches Sa1,Sa2, Sa3 and Sa4 may be common to each of the N parallel-connectedcircuits. The use of common switches, while achieving the samefunctionality, may reduce the size and cost of circuit 10.

Reference is made to FIG. 15 , which illustrates a circuit diagram of anelectrical circuit (e.g., power converter) 150. Electrical circuit 150comprises circuit 151, which is an example of each of circuits A1, A2,A3 . . . and AN, B1, B2, B3 . . . and BN, and C1, C2, C3 . . . and CN ofFIG. 10 , according to aspects of the disclosure. In some aspects,circuit 151 may be a half-bridge converter.

Circuit 150 includes electrical circuit (e.g., power converter) 151 andoutput inductor L150. Circuit 151 includes: switches S41 and S42.

Electrical circuit 151 may be connected across input terminals A and B.(e.g., similar to input terminals A and B of FIG. 10 ). Electricalcircuit 151 may convert the input direct-current (e.g., DC) voltageacross input terminals A and B to an output alternating-current (e.g.,AC) voltage at terminal OUT. Output inductor L150 may be connected toterminal OUT.

Switches S41 and S42 may be series-connected across input terminals Aand B. A first terminal of switch S41 may be coupled to input terminal Aand a second terminal of switch S41 may be coupled to terminal OUT. Afirst terminal of switch S42 may be coupled to terminal OUT and a secondterminal of switch S42 may be coupled to input terminal B.

Switches S41 and S42 may be switched by a controller (e.g., controller980 of FIG. 10 ) in a complementary manner at a second frequency andaccording to a duty-cycle ratio of the output voltage at terminal OUT.The second frequency may be higher than the first frequency. Forexample, during the positive half-cycle of the output voltage atterminal OUT, switch S41 may be switched at a duty-cycle ratio D of theoutput voltage at terminal OUT, while switch S42 may be switched at 1-D.When switch S41 is OFF, switch S42 may be ON, and vice versa. During thenegative half-cycle of the output voltage at terminal OUT, switch S42may be switched at the duty-cycle ratio D of the output voltage atterminal OUT, while switch S41 may be switched at 1-D.

In a case where circuit 151 is used for each of circuits A1, A2, A3 . .. and AN, B1, B2, B3 . . . and BN, and C1, C2, C3 . . . and CN of FIG.10 , all output terminals OUT of each circuit of the same powerconverter (e.g., A1, A2, A3 . . . and AN) may be coupled together, tothe same node of the output inductor of the corresponding powerconverter (for example, output inductor L150). In some aspects of thedisclosure herein, all output terminals OUT of each circuit of the samepower converter (e.g., A1, A2, A3 . . . and AN) may be coupled tomutually coupled inductors (e.g., coupled inductors L4, L5, L6 of FIG. 2), each of which is connected to an output inductor (e.g., differentialfilter), similar to output inductor L7 of FIG. 2 .

In some aspects, circuit 151 may function as a single-phase powerconverter. For example, circuit 151 may replace each of the single-phaseconverter circuits 91, 92 and 93 in FIG. 10 .

It is to be understood that the inventions are not limited inapplication to the details set forth in the description contained hereinor illustrated in the drawings. Other examples of the inventions arecontemplated and the inventions are capable of being practiced andcarried out in various ways. Hence, it is to be understood that thephraseology and terminology employed herein are for the purpose ofdescription and should not be regarded as limiting. As such, thoseskilled in the art will appreciate that the conception upon which thisdisclosure is based may readily be utilized as a basis for designingother structures, methods, and systems for carrying out the severalpurposes of the presently disclosed subject matter.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are described asexample implementations of the following claims.

Those skilled in the art will readily appreciate that variousmodifications and changes can be applied to the examples as hereinbeforedescribed without departing from the scope, defined in and by theappended claims, of the disclosure. Further, various modificationsshould be readily appreciated from the following paragraphs describingvarious combinations of features set forth in numbered clauses.

Clause 1: A system comprising:

a direct current (DC) power source configured to supply a DC voltageacross a pair of input terminals; and an apparatus comprising:

a first plurality of power converters comprising P power converters,wherein each power converter of the first plurality of power convertersis coupled to the pair of input terminals and configured to convert theDC voltage to an alternating-current (AC) voltage at a first frequencyat a respective output terminal;

wherein each power converter of the first plurality of power converterscomprises a second plurality of electrical circuits comprising Nelectrical circuits; and

wherein each electrical circuit of the second plurality of electricalcircuits is configured to switch based on one of a plurality of controlsignals having a second frequency, wherein each of the plurality ofcontrol signals is phase shifted, by 1/(N*P) of a switching period ofthe second frequency, with respect to another control signal of theplurality of control signals and phase shifted, by 1/N of the switchingperiod of the second frequency, with respect to another control signal,of the plurality of control signals, for another electrical circuit ofthe same power converter.

Clause 2: A system comprising:

a direct current (DC) power source configured to supply a DC voltageacross a pair of input terminals; and an apparatus comprising:

a first plurality of power converters comprising P power converters,wherein each power converter of the first plurality of power convertersis coupled to the pair of input terminals and configured to convert theDC voltage to an alternating-current (AC) voltage at a first frequencyat a respective output terminal;

wherein each power converter of the first plurality of power converterscomprises a second plurality of electrical circuits comprising Nelectrical circuits; and

wherein each electrical circuit of the second plurality of electricalcircuits is configured to switch based on one of a plurality of controlsignals having a second frequency, wherein each of the plurality ofcontrol signals is phase shifted, by 1/(N*P) of a switching period ofthe second frequency, with respect to another control signal of theplurality of control signals.

Clause 3: A system comprising:

a direct current (DC) power source configured to supply a DC voltageacross a pair of input terminals; and an apparatus comprising:

a first plurality of power converters comprising P power converters,wherein each power converter of the first plurality of power convertersis coupled to the pair of input terminals and configured to convert theDC voltage to an alternating-current (AC) voltage at a first frequencyat a respective output terminal;

wherein each power converter of the first plurality of power converterscomprises a second plurality of electrical circuits comprising Nparallel-connected electrical circuits; and

wherein each parallel-connected electrical circuit of the secondplurality of parallel-connected electrical circuits is configured toswitch based on one of a plurality of control signals having a secondfrequency, wherein each of the plurality of control signals is phaseshifted, by 1/(N*P) of a switching period of the second frequency, withrespect to another control signal of the plurality of control signals.

Clause 4: The apparatus of any one of clauses 1 or 2 or 3, wherein eachpower converter of the first plurality of power converters is coupled athird input terminal.

Clause 5: The apparatus of clause 4, wherein the third input terminal iscoupled to at least one of a neutral potential, an earth potential, orthe first terminal.

Clause 6: The apparatus of any one of clauses 1 or 2 or 3, wherein acapacitor is coupled between the pair of input terminals.

Clause 7: The apparatus of any one of clauses 1 or 2 or 3, wherein aplurality of series-connected capacitors is connected across the pair ofinput terminals.

Clause 8: The apparatus of any one of clauses 1 or 2 or 3, furthercomprising one or more inductors coupled to a respective outputterminal.

Clause 9: The apparatus of any one of clauses 1 or 2 or 3, wherein eachpower converter of the first plurality of power converters provides asingle phase output with respect to at least one of a neutral potential,an earth potential, or the first terminal.

Clause 10: The apparatus of any one of clauses 1 or 2 or 3, wherein afirst inductor for a first electrical circuit of the second plurality ofelectrical circuits is configured to have mutual inductance with atleast a second inductor for a second electrical circuit of the secondplurality of electrical circuits.

Clause 11: The apparatus of any one of clauses 1 or 2 or 3, wherein atleast one electrical circuit of the second plurality of electricalcircuits comprises a switch.

Clause 12: The apparatus of any one of clauses 1 or 2 or 3, wherein atleast one electrical circuit of the second plurality of electricalcircuits comprises two or more switches.

Clause 13: The apparatus of any one of clauses 1 or 2 or 3, wherein atleast one electrical circuit of the second plurality of electricalcircuits comprises a plurality of series-connected switches.

Clause 14: The apparatus of clause 11, further comprising a controllerconfigured to control the switch.

Clause 15: The apparatus of clause 12, further comprising a controllerconfigured to control the two or more switches.

Clause 16: The apparatus of clause 13, further comprising a controllerconfigured to control plurality of series-connected switches.

Clause 17: The apparatus of any of clauses 14 or 15 or 16, wherein thecontroller is configured to switch a first switch in a complementarymanner with respect to a second switch.

Clause 18: The apparatus of any of the preceding clauses, wherein thecontroller is configured to switch each parallel-connected electricalcircuit of the second plurality of parallel-connected electricalcircuits in a phase-shifted manner with respect to each other.

Clause 19: The apparatus of any of the preceding clauses, wherein thecontroller is configured to switch each electrical circuit of the secondplurality of electrical circuits in a phase-shifted manner with respectto each other.

Clause 20: The apparatus of any of the preceding clauses, wherein thecontroller is configured to switch one of the switch, series-connectedswitches, or the two or more switches, based on a duty cycle ratio.

Clause 21: The apparatus of any of the preceding clauses, furthercomprising a relay connected between at least one of the one or moreinductors and the output terminal.

Clause 22: A method comprising:

converting, by a power converter of a first plurality of P powerconverters, a DC voltage, received across a pair of input terminals, toan alternating-current (AC) voltage at a first frequency at a respectiveoutput terminal, wherein each power converter of the first plurality ofthe P power converters comprises a second plurality of electricalcircuits comprising N electrical circuits; and

switching (e.g., sequentially shifting) the second plurality ofelectrical circuits based on a plurality of control signals having asecond frequency, wherein each of the plurality of control signals isphase shifted, by 1/(N*P) of a switching period of the second frequency,with respect to another control signal of the plurality of controlsignals.

Clause 23: A method comprising:

converting, by a power converter of a first plurality of P powerconverters, each comprising a second plurality of electrical circuitscomprising N electrical circuits, a DC voltage, received across a pairof input terminals, to an alternating-current (AC) voltage at a firstfrequency at a respective output terminal; and

controlling each electrical circuit of the second plurality ofelectrical circuits based on a plurality of signal having a secondfrequency, wherein each of the plurality of signals is phase shifted, by1/(N*P) of a switching period of the second frequency, with respect toanother signal of the plurality of signals and phase shifted, by 1/N ofthe switching period of the second frequency, with respect to anothersignal, of the plurality of signals, for another electrical circuit ofthe same power converter.

Clause 24: A method comprising:

converting, by a power converter of a first plurality of P powerconverters, each comprising a second plurality of series-connections ofswitches comprising N series-connections of switches, a DC voltage,received across a pair of input terminals, to an alternating-current(AC) voltage at a first frequency at a respective output terminal; and

controlling each of the series-connections of switches based on aplurality of signals having a second frequency, wherein each of theplurality of signals is phase shifted, by 1/(N*P) of a switching periodof the second frequency, with respect to another signal of the pluralityof signals and phase shifted, by 1/N of the switching period of thesecond frequency, with respect to another signal, of the plurality ofsignals, for another series-connection of switches of the same powerconverter.

The method of any one of clauses 22 or 23 or 24, further comprising oneor more features of any of clauses 1-21.

1. An apparatus comprising: a pair of input terminals configured tosupply a direct current (DC) voltage; a first series connectioncomprising a first capacitor and a second capacitor, wherein the firstseries connection is connected across the pair of input terminals, andthe first capacitor is connected to the second capacitor at a firstterminal; and a plurality of power converters, wherein each powerconverter of the plurality of power converters is coupled to the pair ofinput terminals and configured to convert the DC voltage to analternating-current (AC) voltage at a first output frequency at arespective output terminal; wherein each power converter of theplurality of power converters comprises: a second series connectioncomprising a first switch, a second switch, a third switch and a fourthswitch, wherein the second series connection is connected across thepair of input terminals, wherein the first switch is connected to thesecond switch at a second terminal, wherein the second switch isconnected to the third switch at a third terminal, wherein the thirdswitch is connected to the fourth switch at a fourth terminal; and aplurality of circuits, wherein each circuit of the plurality of circuitscomprises: an additional series connection comprising two or moreswitches across the second terminal and the fourth terminal and anintermediate node between the two or more switches of the additionalseries connection; and a leg comprising an inductor having mutualinductance with another inductor of another leg, wherein the leg isconnected between the intermediate node and an output terminal.
 2. Theapparatus of claim 1, wherein the first terminal is connected to thethird terminal.
 3. The apparatus of claim 1, wherein the output terminalprovides a single phase output with respect to at least one of a neutralpotential, an earth potential, or the first terminal.
 4. The apparatusof claim 1, further comprising a controller configured to switch thefirst switch, the second switch, the third switch, and the fourth switchof each power converter of the plurality of power converters at a firstswitching frequency, and to switch, based on one of a plurality ofcontrol signals, each circuit of the plurality of circuits at a secondswitching frequency.
 5. The apparatus of claim 4, wherein each of theplurality of control signals is phase shifted, by 1/(N*P) of a switchingperiod of the second switching frequency, with respect to anothercontrol signal of the plurality of control signals, where N is thenumber of the plurality of circuits and P is the number of the pluralityof power converters.
 6. The apparatus of claim 5, wherein each of theplurality of control signals is phase shifted, by 1/N of the switchingperiod of the second switching frequency, with respect to anothercontrol signal, of the plurality of control signals, for another circuitof the plurality of circuits of a same power converter of the pluralityof power converters.
 7. The apparatus of claim 4, wherein the controlleris configured to switch the first switch of the corresponding powerconverter of the plurality of power converters, in correspondence withthe third switch of the corresponding power converter, and in acomplementary manner with respect to the second switch of thecorresponding power converter.
 8. The apparatus of claim 4, wherein thetwo or more switches of the additional series connection comprises afifth switch and a sixth switch, and wherein the controller isconfigured to switch the fifth switch and the sixth switch in acomplementary manner.
 9. The apparatus of claim 4, wherein thecontroller is configured to switch a circuit of the plurality ofcircuits of the plurality of power converters in a phase-shifted manner,by 1/(N*P) of a switching period of the second switching frequency, withrespect to another circuit of the plurality of circuits of the pluralityof power converters, where N is the number of the plurality of circuitsand P is the number of the plurality of power converters.
 10. Theapparatus of claim 4, wherein the controller is configured to switch thetwo or more switches of the additional series connection, based on aduty cycle ratio.
 11. The apparatus of claim 1, wherein each leg of theplurality of circuits further comprises a relay; and wherein theapparatus further comprises: a controller configured to open or closethe relay based on an output of a sensor configured to measure a currentof the inductor of the same leg.
 12. The apparatus of claim 1, furthercomprising a controller configured to control, based on one or morecurrent measurements for a first inductor of a first circuit of theplurality of circuits or a second inductor of a second circuit of theplurality of circuits, a first current of the first inductor or a secondcurrent of the second inductor to balance the first current with thesecond current.
 13. The apparatus of claim 12, wherein the controller isconfigured to receive the one or more current measurements from one ormore sensors and to control the first current of the first inductor orthe second current of the second inductor to balance the first currentwith the second current by changing one or more pulse width modulationsignals.
 14. The apparatus of claim 1, wherein the first seriesconnection comprises a third capacitor connected in parallel with or inseries with the first capacitor across the pair of input terminals. 15.A system comprising: a direct current (DC) power source configured tosupply a DC voltage across a pair of input terminals; a first seriesconnection comprising a first capacitor and a second capacitor, whereinthe first series connection is connected across the pair of inputterminals, and the first capacitor is connected to the second capacitorat a first terminal; a plurality of power converters, wherein each powerconverter of the plurality of power converters is coupled to the pair ofinput terminals and configured to convert the DC voltage to analternating-current (AC) voltage at a first output frequency at arespective output terminal; and a controller; wherein each powerconverter of the plurality of power converters comprises: a secondseries connection comprising a first switch, a second switch, a thirdswitch and a fourth switch, wherein the second series connection isconnected across the pair of input terminals, wherein the first switchis connected to the second switch at a second terminal, wherein thesecond switch is connected to the third switch at a third terminal,wherein the third switch is connected to the fourth switch at a fourthterminal; and a plurality of circuits, wherein each circuit of theplurality of circuits comprises an additional series connectioncomprising two or more switches across the second terminal and thefourth terminal and an intermediate node between the two or moreswitches of the additional series connection; and wherein the controlleris configured to: switch the first switch, the second switch, the thirdswitch, and the fourth switch of each power converter of the pluralityof power converters at a first switching frequency; switch, based on oneof a plurality of control signals, each circuit of the plurality ofcircuits at a second switching frequency; and switch a circuit of theplurality of circuits in a phase-shifted manner, by 1/(N*P) of aswitching period of the second switching frequency, with respect toanother circuit of the plurality of circuits, where N is the number ofthe plurality of circuits and P is the number of the plurality of powerconverters.
 16. The system of claim 15, wherein the first terminal isconnected to the third terminal.
 17. The system of claim 15, whereineach circuit of the plurality of circuits further comprises: a legcomprising an inductor having mutual inductance with another inductor ofanother leg of a same power converter, wherein the leg is connectedbetween the intermediate node of the same circuit and an outputterminal.
 18. The system of claim 17, wherein each leg of the pluralityof circuits further comprises a relay; and wherein the controller isconfigured to open or close the relay based on an output of a sensorconfigured to measure a current of the inductor.
 19. The system of claim15, wherein the controller is further configured to control, based onone or more current measurements for a first inductor of a first circuitof the plurality of circuits or a second inductor of a second circuit ofthe plurality of circuits, a first current of the first inductor or asecond current of the second inductor to balance the first current withthe second current.
 20. The system of claim 19, wherein the controlleris configured to receive the one or more current measurements from oneor more sensors and to control the first current of the first inductoror the second current of the second inductor to balance the firstcurrent with the second current by changing one or more pulse widthmodulation signals.